There were lots of good comments to yesterday's Open Friday question. Thanks to everyone who took the time to share their thoughts.
I personally see clones serving two purposes. The first is to provide a legal means to support older RPGs that are no longer in print. While this primarily benefits publishers who want to sell new supplements or adventure modules, it's also quite useful to hobbyists who want to post such things to blogs, websites, or forums. Remember how TSR treated online resources produced by amateurs in the 90s? Retro-clones, operating under the OGL, obviate that concern. The second purpose is to ensure that, rather than relying a dwindling supply of older gaming materials, newcomers can purchase old school RPGs easily and cheaply.
As time goes on, it's inevitable that the retro-clones will replace the original games of which they are clones. As I mentioned above, there are a finite number of original games still available for purchase and that number will only decrease with time. You can already see this principle in action with regards to OD&D, whose LBBs and supplements are both increasingly hard to acquire and to acquire without spending a small fortune. Twenty years from now this situation will only be worse. This is why I'd like to see more close clones of older games rather than games inspired by them. I have no objection to original games that draw on older ones for inspiration, but, without close clones, certain games will become ever more inaccessible to players who lack access to the originals.
I'll add that, while I think it'd be terrific if WotC again made older products available in PDF form, their doing so doesn't affect retro-clones in any way. The ability to get hold of Moldvay/Cook again would be great, but I wouldn't ditch Labyrinth Lord if it ever happened. Why? Well, I seriously doubt that WotC would release its older materials under any form of open license and, yes, one can legally make support materials for these materials without an open license, it's less legally safe than doing so under the auspices of something like the OGL. More importantly, a PDF, useful as it can be, is no substitute for a printed product. Without actual physical books available from your local hobby store, you can't easily attract many newcomers to these games, thus the need for retro-clones.
Now, some old schoolers don't actually care about attracting newcomers. They're quite content in their existing gaming group and online communities and, for them, retro-clones, PDFs, and support materials are only important to the extent they support them and their interests. I can understand, even respect, that position, but it's not one that I share. I have no illusions that the ongoing old school renaissance is going to make tabletop RPGs, let alone old school ones, mainstream again the way they were in the 80s. We're never again going to see 12,000 copies of any game being sold each month. I'm fine with that. Nevertheless, I think it's vital that close clones of many of these older games exist and be available in local game stores. Without them, this segment of the hobby is only going to shrink further and I certainly don't want that. For me, clones are a way to ensure a future independent of the whims of game companies.