The term dream can be misleading, because in these games the dreams of the Fayth can be corporeal.

DZ and Zanarkand ruins are two different locations that exist at the same time but not in the same place. Both the player and Tidus are mislead to thinking he's traveled in time for 90% of the game.

So he's as real as anyone else so long as Yu Yevon continues the summon. Once he's defeated DZ (and everyone in it including Tidus) cease to exist-corporeally at least.

If you consider FFX-2 canon, then Tidus spent some time without a physical body. As for the sequel itself, I'm of two minds:

1) It's unecessary since FFX ended on the perfect bittersweet note. It's a game-length excuse to give you a Wayne's World-style 'mega-happy ending'.

2) The gameplay is great, the battle system innovative and I liked the new characters that got introduced. Too bad the carryover characters didn't do so well.