For some of those players, I feel like your houserule would actually slow down combat even more, as their options multiply.
First of all, thanks for your positive reply. Second of all, I think it won't slow them down for the same reason our ranger in my party just ignored all his other exploits to focus just on a single one that was very effective at combat; that was called Twin Strike. With this new rule, almost every at-will power of every class has the potential to become a "Twin Strike" (for a cost of course). Think about it... all those people who just don't want to mess with dozens of powers and abilities can finally focus on their at-wills and be relatively effective at combat regardless of their class. Of course, they will never reach the level of effectiveness of the more sophisticated 4th edition players but they will probably be able to stand their ground and deliver either blows that (almost) always hit or that (almost) always deal tons of damage. And all this just with their at-wills.
Post if you wish to ask about Ruins & Raiders. I do not answer to PMs anymore.