It does feel like you left something behind, and in part, you have. All those save games, readily available DD games, friends etc. Every time I've been on my JP account to play a demo, I've wanted to go back to my EU one so that I can play any game on a whim.
Out of curiosity, what US exclusive games are you playing on it?
Well they're not all US only. For example Parasite Eve 1 is not on the UK store, but the 2nd and 3rd games are. Thought it was easier to just get them all on the same profile, hence via the US Store. And some games like Valkyria Chronicles 2 and FF Tactics: WotL I just got because I had a lot of spare cash in my US account. Kinda regret those now...
Then there's others like Suikoden, Growlanser. The two Secret Santa gifts from Toma in Legend of Mana and Breath of Fire IV. Kinda feel like playing Chrono Cross and Xenogears again, but I probably won't this time around. Will leave it for the next time I'm on my US account.
I don't have PS+ on the either on the US, so it feels strange in that there's something that just don't happen automatically on Vita. Kinda got used to seeing several notifications whenever I put my Vita on in the morning. Messing around in the Live Area isn't fun anymore...
Allowing mutiple account a la PS3 would be my most wanted Vita update