I agree with that because of the legroom. The main point here is that VX MCS has the same legroom as UA F. Furthermore, the free food and drinks are a significant bonus. My point is just that is is closer to UA F than UA Premium Economy, so free upgrades to MCS are worth a lot. The only thing that you are missing for UA F is the seat width (and they are still wider than UA Premium Economy)

Also, with status, you can pick the front EE row, which has the same legroom as MCS, but doesn't recline (which is why they are MC and not MCS seats). There isa $30 fee to select that seat at booking time, so they are almost always available (even the windows). But you don't have to pay the fee if you have status. So if you want a cheap window seat with legroom, that is always an option.

Personally, I just buy F outright (not upgrades). I find that with the points that I get (10 pts/$ for being gold) it's really not worth it to try to save a few dollars by hoping to be able to buy an upgrade (since you don't get any pts on the upgrade fee). The extra points often offset the potential savings, and you are guaranteed to get the sear. I can usually get the deepest-discount F fares so they really aren't very expensive (I fly mostly short-hauls; I realize that F is much more expensive for transcontinental flights)