Disclaimer: This is based on my personal experience after a single day of play (~5 hours), along with reading all the various reviews and posts. If my observation of how coin payouts works is incorrect, feel free to let me know so I can amend this post.
It seems the one universal gripe that anyone can lay on this otherwise awesome game centers around the coin system that is implemented. (OK, the requirement to be always connected to the internet is another valid one, but let's stay focused). The feeling is that this system is restrictive to playing the game the best way possible, that is, playing the game with the goal of achieving a high score. Why? Because the number of coins you must spend to run with 3 power-ups is prohibitively expensive when compared to the coin payout the song delivers.
Hear me out here. To run with 3 power-ups costs 750 coins (200, 250 and 300 is what I'm going off of with memory - if those numbers aren't right, let me know). It appears that songs pay out coins based on the song's length. I base this assumption on the fact that I can 4 star two songs, and get paid different amounts (200, 300 or 400 was mostly what I saw when playing through the songs included with blitz plus a few others).
This means that if you want to put a competitive score on the leaderboards, you're doing so at the cost of 550, 450, or 350 coins a pop. Sure, you get a bonus the first time you play a new song that helps offset this, but in 6 months, when you've played your library and the only thing left is high scores, you'll have to grind a song 2 or 3 times to get the coins necessary to do a single scoreboard run.
This grinding goes against what I think could make Blitz shine - the feeling that every time you play a song, you could post a high score. The game should be rewarding experimentation with different powerups, not making people hoard coins and save them for when they're doing score battles.
The latter is exactly what I was doing most of the night last night - I was consistently getting mid 4-stars on songs because I refused to use powerups on a first playthrough. I just felt it was a waste of coins, and I knew I'd need those coins for Score Wars later (which I did). I still had fun, but the leaderboard postings became almost frustrating because I knew I could post better, but I was reluctant to burn coins to do it.
So what is a reasonable solution to still make coins have a value, but remove the sense of grinding?
Double the coin payout for any song that gives 300 or more. This will immediately add value to songs that have some length (since very short songs will still payout only 200, which makes them less ideal for coin grinding), while also encouraging power-up usage in songs, since the deficit is reduced significantly. I still think there should be some deficit - there needs to be something to prevent people from just running a song with minimal effort to get coins - but this way the leaderboard will start becoming filled with competitive scores, instead of a hodge-podge of grind scores mixed with high score runs.
So what happens to the coin distribution now? Song payouts become 200, 600, 800. Cost is still 750, so I think it may be worth bumping up the values of at least 2 of the powerups by 50 coins, making them, say, 250, 300, 300, or 850 to run with all 3.
This makes the coin deficit for current 200/300/400 songs as 650 (instead of 550), 250 (instead of 450), and 50 (instead of 350). This is still pretty punishing to extremely short songs, but cuts the deficit for other song lengths to values that I think are more manageable, and makes every song run high score worthy. Songs of longer lengths may have even higher payouts that actually create a net gain in coins, which is fine.
To manage the costs of short songs when playing them for competitive reasons, perhaps a song that rewards 200 coins could offer a bonus 200 coins if the song was played with all 3 powerups (so grinders will still need to spend coins to get coins) - thus cutting that deficit to 450 (still better than the current 550).
Additional consideration can be made for quality of the run - more stars = more coins at the given level. I think this should be a bonus applied after the doubler for 5 gold star runs only (perhaps an additional 100 coins).
This alternative solves a lot of problems at once: People who want their scores to be competitive can do so without bankrupting themselves as quickly. People will be more willing to experiment with various powerups. And, most importantly, people will come to utilize the Facebook app more organically, rather than feeling forced to in order to have enough coins to do anything. There's a lot of (perhaps unwarranted) negativity towards the feeling of having to have the Facebook app to keep up with the coin spend. This solution would solve that to some extent, and make the Facebook app a fun way to expand on the game, rather than an evil overlord requirement.
Whew.. that was a lot longer than I thought - sorry. Thoughts?
tl;dr: Double coin payouts for all songs that payout 300 or more coins. Increase coin cost of 2 powerups by 50 coins. This lessens the deficit overall, and encourages competitive scores while discouraging grinding short songs for coins.