Long story short: the Sages' enactment to marry a virgin on Wednesday doesn't apply anymore, and we can get around the reason to marry a widow on Thursday.
However, there are a bunch of days that are ideal to get married, and a bunch of days that are recommended not to get married. The list is quite lengthy, so I'll leave that for another question, as you were specifically asking about the Mishnah. Below are the details relating to that.
Marrying a virgin on Wednesday
There are two reasons why the Mishnah regarding a virgin isn't followed anymore. First, some background into the Mishnah.
The custom in the times of the Sages was for a couple to enter the first stage of marriage known as erusin, translated as betrothal, and a some time later enter the final stage known as nisuin. For a virgin the time lapse was a year, and a widow was thirty days (Kesubos 5:2 with Bartenura). During the period of erusin, the couple are legally married and it would be adulterous to have relationships with others, but they are not yet living together. From nisuin onwards, the couple lives together.
The Mishnah you cite is discussing when to perform nisuin. The reason a virgin is to be married on a Wednesday is as follows. The Sages were concerned that the man will marry her, and while consummating the marriage will come think she wasn't a virgin (ie: she committed adultery during erusin). He would then go to Beis Din, the Jewish court, and accuse her of adultery. The matter will be investigated and settled. However, if there would be a time lapse between their marriage and the next court date, he might cool off and end up staying with her, even if she really did commit adultery (making her forbidden to him) (Rashi to Kesubos 2a).
The Beis Din used to regularly meet on Mondays and Thursdays. To avoid any time lapse, the Sages mandated that all virgins be married on Wednesday, so that they'll consummate the marriage Wednesday night. If he has suspicions, he'll run to Beis Din the next morning. Why not also get married on Sunday, so he can run to Beis Din on Monday? The gemarra gives two reasons. One is so that he'll have at least three days to prepare the wedding feast (Kesubos 2a). The other is if they consummate the marriage Wednesday night, that's an auspicious time, as it will be yom chamishi, the fifth day of the week. That was when Hashem blessed the fish that they should be fruitful and multiply (Genesis 1:22) (Kesubos 5a). Tosafos to Kesubos 2a clarify that the main reason is the first one, and the second reason is just good advice.
The gemarra (Kesubos 3a) says that if the Beis Din meets every day, then a virgin can get married any day. That's on condition that they adequately prepared the wedding feast ahead of time. That's one reason why weddings aren't specifically on Wednesdays for virgins. Since the Beis Din doesn't specifically meet on Mondays and Thursdays anymore, the enactment of the Sages doesn't apply.
The Tur Even HaEzer § 64 writes this explicitly:
ובזמן הזה שאין זמן קבוע לישיבת ב"ד יכול לישא בכל יום שירצה מימות החול ובלבד שיהיה לו צרכי סעודה מוכן
These days, that there isn't a specific time for Beis Din to convene, a person can get married any weekday they please, so long as they've adequately prepared the wedding feast in advance.
The second reason is that as mentioned, the custom in the days of Chazal was to have a year gap between erusin and nisuin. Since our custom today is to do both at once (Rema, end of Shulchan Aruch Even HaEzer 55:1), the whole reason for concern never gets started, as she couldn't commit adultery before nisuin (Darkei Moshe 64:4; Be'ur HaGra 55:11). As such, there's no reason for the enactment to specifically get married on Wednesdays.
Marrying a widow on Thursday
Regarding a widow, which the Mishnah says should be married on a Thursday, the gemarra gives two reasons. The first reason is if they get married on Thursday, they'll consummate the marriage Thursday night. That will be yom shishi, the sixth day of the week, which is an auspicious time, as it's when Hashem blessed Mankind that they should be fruitful and multiply (Genesis 1:28) (Kesubos 5a). The second is because the Sages were concerned that someone who marries a widow will leave her the next day to go to work. To give the new couple adequate time together, the Sages said they should get married on Thursday. As such, they'll perforce have three days together: Thursday, Friday, and Shabbos (ibid). The gemarra says the difference between the two reasons is someone who doesn't have to go to work. According to the first reason, they should still get married on Thursday. According to the second reason, they can get married any day. Tosafos ad. loc. again say the main reason isn't the blessing reason but so he doesn't leave her for work.
It would come out then that someone who has to work should have to marry a widow on Thursday. However, we don't find this in the poskim. In fact, people seem to marry widows any day they want (Aruch HaShulchan Even HaEzer 64:7). Perhaps it's because the Mishnah which said to marry a widow on Thursday wasn't an absolute rule, just the Sages telling us what is appropriate (Mishneh Torah Hilchos Ishus 10:15, brought by the Shulchan Aruch Even HaEzer 64:3, as explained by the Aruch HaShulchan). The Aruch HaShulchan (loc. cit. § 9) explains that perhaps since it became the norm to spend three days together after marrying a widow, people continued to not go to work after getting married, even if it was on a different day of the week. However, the Tur seems to write that anyone who has a job should marry a widow on a Thursday. Perhaps then the custom to marry any day is because the widow has the ability to forgive her due rights. However, this still requires further investigation. Regardless, if they discussed ahead of time that he'll be going to work right after they marry, it would definitely be permissible (Aruch HaShulchan loc. cit. § 10).
Why not marry on Thursday to receive the associated blessing?
Regarding the auspicious time to get married due to the blessing associated with that day, it would still seem appropriate to get married on a Thursday, associated with the blessing to Mankind (as the gemarra says that blessing is better than the blessing to fish (Kesubos 5a)). Indeed, the Penei Yehoshua Kesubos 2a Kuntres Acharon § 1, brought by the Pischei Teshuvah ad. loc. § 6, and Torah Temimah to Genesis 1:22 § 57, express surprise at the poskim for not mentioning this. They say it would be best to try to get married on this day, due to the blessing associated with it. However, people do not seem to be concerned with this, as noted by Rav Moshe Feinstein in his Igros Moshe Even HaEzer 1:93.