This reminds me that now is a good time to buy a PSP on the Cheap. Trying to remember which is the best model out of the 3, not the PSP Go of course.
Also, the thing with the Vita like with anything when first release is that it is overpriced and the hardware has not been tested for a year of use yet. As for the memory card problem, it isn't all that bad really. The main titles are their own game cards and I seriously doubt most early release downloadable only titles will go past 200-300MB for the most part. So a 4GB-8GB should be fine unless you seriously need to store every PSP download you own on your VITA.
If the system isn't selling as they plan, which will be the case... then later on the prices will go down, a second revision will come out, more than likely a standard memory format will be added to the revised model and this will be the time when downloads titles become bigger files. The proprietary cards will also go down in price in a year, even if they don't switch to standard memory cards with a revised model.
Just wait a bit, I never buy any console/handheld hardware on release. I have gotten burned too many times with consoles running into problems with hardware failures, lack of options, limited selection of games and paying too much. When you wait, you actually have good games to play. Seriously, the PS3 wasn't really worth me buying until 2008 game-wise. Of course, I didn't get around to buying it till January 2011. I am glad I put it off, since the PS3 Slim 160GB was exactly what I wanted and even more games like Heavy Rain, Uncharted 2, etc... were out.