My proposal does this:
Lowers the minimum cap (so the smallest teams can sit on theri cash if they like)
Keeps a relatively similar tax threshold
Has teirs of tax penalty for teams who go above
If your caps are 100m minimum, 150 tax threshold and a sliding scale from there that makes it very hard to spend drastically more than the other teams. Here's an example of what I think 32 teams would probably look like
4 teams between 100 and 110M
6 teams between 110 and 120M
8 teams between 120M and 140M
8 teams between 140M and 150M (pack would be here, spending just less than the top teams, but still could break the threshold if they thought they were on teh cusp)
4 teams between 150M and 160M
2 teams between 160M and 180M
Obviously this is just a starting point, the % and numbers will change, but this is the concept. Teams who want to skimp can skimp (but only to a degree). Teams who want to do everything in their power to win, will be able to because nobody is spending drastically more than anyone else. And teh teams with the most money can spend it, keeping the most popular teams a little more relevant.
Over the long run, I think this plan brings parity and a slight advantage to the largest markets. I think that grows the pie larger because it keeps the most fans interested more of the time, while still keeping the lower teams relevant.
As far as the players concerns, when they get more money, it's really coming at expense of the richest teams. Make those rich teams feel like their getting something for their money rather than sharing so much and the motivation to pay more goes up too.