Modern movies toys aren't worth a lot unless they were exclusive, hard to find, limited repaints, retools, etc. For example I bought a Revenge of the Fallen Bruticus combiner, which was a Target exclusive, for $7.48 on clearance (75% off) and sold it (was MISB) for almost $300 on ebay in 2011. But stuff like that is the exception. Mass retail release figures can be found rather cheap on ebay, craigslist, forum boards, etc.
If you are talking G1 stuff that you have, theres always a market for that whether its still MIB or opened. If it's in good condition someone will buy. Even if its not in overall good condition someone may buy it for parts.
G1 reissues can go for decent money depending on the figure. Same with Classics/Universe/Generations figures, especially exclusives (Skywarp, Ultra Magnus). Of course Masterpiece figures, because they are so limited, can fetch a pretty penny. Figures that hit in low numbers and never see broad release can go for good money. Scout class (Reveal the Shield I believe) Windcharger only hit in limited numbers (always happens when they switch from movie line or animated line to classics, generations, etc, or a line or figure is "canceled") reports at that time showed that Windcharger was hittinf Ross, Marshalls, etc. for $4.99 (couple bucks cheaper than what MSRP mass release would've been) then they went for $30 - $40 on ebay.
As far as cleaning, I just went through a lot of my collection in recent weeks. For items that were dusty I just ran them under some lukewarm water, used the sink hose, and set them out to air dry on a towel.
I don't think its collectors in your area buying up everything movie related. The only things being scooped up are thing being shipped in low case number assortments.(Hound, Galvatron) But again it comes back to distribution problems and right now its in combination with stores doing summer resets. Everywhere I go, and what I hear from fellow collectors her in California, even deluxe figures are in low quantity. A lot of the other crap, the one step, easy changers (look almost identical to movie deluxe), stuff marketed to kids, just clogs pegs. Right now the last deluxe wave of Generations seem to be shipping and inexplicably the Fall of Cybertron, legend class "cassettes". I think Hasbro may have been playing things a bit safer with movie distribution this time around based on the failings of Dark of the Moon.