I've been trying to compose a sensible answer to this one (with respect to PL running costs) for while now, and can't really get past the following...
Shorten the PL season.
Whilst we can't be 100% sure of this, everything I've seen points to "gammy weather means smaller crowds". Lets face it, March isn't exactly the nicest time to be outside, and it's not the most reliable time of year to run meetings...and rain-offs cost money. Why start the "proper" season in March? It really does strike me as pointless. Sure, there's nothing wrong with a few challenge matches, open meetings and Things of that Ilk at that time, but only where the promotions in question have got their financial sums right.
For my money, the PT also needs looking at. I find it somewhat odd that a competition should be run that creates so many "dead rubber" fixtures right at the start of the season. By my reckoning, a good 30% of PT group stage fixtures are little more than an opportunity for riders to pick up injuries before the main event of the PL itself. I can't be bothered to work it out (and don't have the information anyway...) but there're certainly a few teams out there each year who have their league compaign scuppered before the start thanks to injuries in the PT group stages. Okay, there's little we can do to stop teams loosing "star" riders early in the season, but it always seems odd to me that they should be lost during a Mickey Mouse warm-up event.
T2T, I'd *love* to see restrictions on foreign riders in the PL. There are far too many foreign never-will-bes there at the moment, and this hurts both the chances of young Brits, and the pockets of promoters. The problem is EU employment law prevents this (I think...). Maybe a meaty average reduction for British riders could be introduced somehow?
With regard to removing GP riders from the EL, I think that would be a serious backward step. I can't think of any other sports where you can see such a high percentage of the best competitors in the world competing week in, week out in this country. The GP riders provide Sky with a link between GP events and their league coverage, which is definately a positive step as far as promoting the sport to those who aren't already into speedway. The other danger with a GP rider ban is the loss of rider income - I wouldn't be at all surprised if GP places were rejected by some riders in favour of EL rides in much the same way as some riders spurn the EL in favour of a much more predictable income in the PL. Personally I consider the GP series to be one of the big successes of the modern era, and would hate to see it undermined by the "pricing out" of riders.