First off, let me say this: "Don't knock it til you've tried it."
Second, if even if the game doesn't appeal to you... what about the songs? You do know that you CAN export to Rock Band 3 at NO ADDITIONAL COST (i.e. FREE EXPORT if you purchase the game).
And third, I DARE YOU to find 8 songs that you want the most out of the 25 songs the game comes with. Why do I ask this? Assume that all 25 songs were to be released as singles, it would cost $2 (160 Microsoft Points) per song. So...
25 x $2 (160 Microsoft Points) = $50.00 (4000 Microsoft Points)
To get ALL 25 songs as singles, it would cost $50.00 (4000 Microsoft Points)! But that isn't the case.
Now pick only 8 songs that you want the most...
8 x $2 (160 Microsoft Points) = $16 (1280 Microsoft Points)
Well that isn't the same price of the game, so lets do it this way: Pick only 7 songs that you want the most at a cost of $2 (160 Microsoft Points) and 1 more at a cost of $1 (80 Microsoft Points)...
7.5 x $2 (160 Microsoft Points) = $15 (1200 Microsoft Points)
So... at the cost of $15 (1200 Microsoft Points), you get a new game, the the 8 songs you really want the most, 17 songs for free, and free export to Rock Band 3.
AND DID I MENTION that we are still waiting for the announcement of the remaining 6 songs? Yes, that's right... we only know what 19 of the 25 songs are (at the time of this post).
Personally... I've already found enough songs to make the purchase of Rock Band Blitz worth it.