Miles posted yesterday without having to call. They posted as "50% of miles flown - Main Cabin" instead of "150% of miles - First Class". Sorry if this is a stupid question but is that how it works, that I get the miles for my original ticketed class even though I upgraded and flew F?

Yes that its how it typically works.

Thanks everybody for your input. Just for reference in case people find it useful, I wound up buying MCS (Y+) tickets and tried the T-6 upgrades on BOS-SFO Friday (VX357) and SFO-BOS Sunday (VX352). Ironically I managed to bag a $169 upgrade to F on VX357 (BOS-SFO), took the last available seat at T-6; but failed to secure the last F seat on VX352 because I was half an hour late (tried at T-5.5), which was surprising given that T-6 was around 0330 Sat night / Sun morning!

That said, I think MCS (Y+) is a very good product in terms of both the hard and soft product, and I was almost as happy on Y+ as I was in F on the outbound flight.