I'm not sure that a few free items will do this
That's because they won't, right.
I doubt that anybody has any problems with adding custom belt+ obj items and even making them cost 1 TC just to reward those who got lots of qi, but it's not going to be the "incentive" you're talking about, Hax. I do know lots of custom belts and several items won't make them play more. If you're not one of those guys who farm 200 games daily just to get higher belt, by the time you've got custom belt you already have everything you need if you still care about items. Having items that are only available at 30k / 40k / 50k or 100k qi will be just a neat reward for players, not the reason to play.
Permanent TC boosters are an awful idea and you should know why.
Exclusive colors are also a not the best idea and being an ex-ninja you should also know why.
By the way, you're kind of wrong thinking that the more people play the game the more real money they are likely to spend on it. Most of the stuff is bought by those who've got less than 3k qi, others either buy TC from other players because the "black market" prices are lower or duel the TC to get stuff. There are rare exceptions for USD-only items and forum subscriptions, but still high-qi users tend to buy less.