I look at this a bit different, and agree with amanamanman (try typing that for the first time)
You can't lump everything into one absolute category. Like anything else there are some comics that have increased in value/price, some have stayed the same, some have declined. I feel that over time, like anything else as collectors fill holes in their collections the supply diminishes, however with anything that has large print runs there's a lot out there (look at album covers.. everyone thinks that because they have a mint album cover from 1960 that it's worht a fortune, but when you see "X" million sold, well there you go.. there's millions of them on the open market.
You can't lump comics in with other collectibles either. Just because there's a limited run of something doesn't make it more valuable. 1st prints tend to still be what many (not all) look for in the print medium, so many of those limited editions that get thrown out into the market aren't worth a ton (but again, some do go for some really decent $$$, just like anything else).
Also, when you look at comics that only SOLD for about $3 retail (and in many instances you could get for less back in the days) While you may see a set of Dark Empire sell for say $100 (just making that # up) While it's a lot more than the $24 the set may have originally sold for, it's still very affordable, and again, most collectors have already filled that hole int the collection, so I wouldn't say it's LESS desirable, it's just that SOOOOO many more SW comics (thousands), and stories (even the books for that matter) have come out since that it's easy to become one small part of a much larger whole.