Hundreds of clients still use CS2, but we want to upgrade--what to do?

Question

I know InDesign backwards compatibility and version conversion (or lack thereof) can be a contentious subject, and I know it's been discussed here at great length (http://forums.adobe.com/thread/641138?start=0&tstart=0), but I thought it might be worth a try to present my production department's dilemma. What to do when InDesign CS2 is getting more and more buggy on our Macs, but moving to CS5 would make our files unusable for most of our clients?
We've been putting off dealing with this issue as long as we could, but it's becoming more and more urgent as Adobe releases new CS versions.
The details:
I'm the production manager/art director for a small inhouse art department. We have 5 art department Macs and 7 editorial department Macs running CS2 (InDesign, Illustrator and PhotoShop) in 10.5 or 10.4, depending on the Mac.
Our company sell and distribute editable InDesign CS2  files (puzzles, graphics and so forth) to hundreds of clients around the world, most of whom are newspapers.
It'd be really nice if they'd upgrade, but newspapers are cutting their budgets and laying off staff left and right, and they're certainly not about to upgrade if they can avoid it. Seriously: a large percentage of them are still using Quark 4 in Mac Classic, which we can't support, so they have to recreate the puzzles from scratch using text and eps files. (The puzzles we still distribute as Quark files we have to create in 6.5 and backsave to 5, though I realize there is software out there from Marksware that could solve this problem.)
I'd love to just give them PDFs... But these files need to be editable so that the newspapers can change them to match their own fonts and styles, or edit them to fit, or translate them into other languages. (We create them with generic fonts such as Helvetica and Times that all newspapers are bound to already own, since we can't distribute fonts along with the files).
Meanwhile, as our own computers get upgraded or replaced, InDesign CS2 is causing more and more issues--it crashes all the time, doesn't work right in Snow Leopard (we had to downgrade back to regular Leopard), and of course won't open files created in later versions, since someone with CS5 or CS4 can't backsave to CS2.
So what are the possible solutions? Has anyone else dealt with this? What have you done? Some things I've considered:
Trying to create editable PDFs... but many of the clients we have are not particularly tech-savvy, and I have to admit I'm not sure how to do this in an efficient and user-friendly way.
Buying CS5 for just department, and digging through eBay and other channels to buy just enough copies of CS3 and CS4 to use as a bridge back to CS2. But this just seems like such a clunky and inefficient solution that would significantly slow down all those nice production workflows I spent so much time streamlining.
Letting clients know that the oldest version we could support is CS3. But that still leaves the problem that we'd have to get a bunch of copies of CS4, which is no longer the latest!
Sigh... this is driving me nuts! Any suggestions are appreciated!

Answer 1

Thank you all for your responses! Peter, you're correct that I did already pretty much know the answer, but I was hoping there was just some trick or solution out there that we hadn't thought of that other InDesign users had come across.
We are indeed trying to hold on to and maintain some older Macs for using CS2, and even have a Mac still running Classic for Quark 4 (oh, and Pagemaker--my goodness, I forgot about all our Pagemaker documents!). And I'll talk to the  folks here about setting up a more robust long-term technology plan.
Bob, you are also correct that in hindsight my company probably should have bought each version as it came out, and maybe we will do that going forward.
But I have to say I'm still frustrated that no third-party conversion app exists, especially since the files we create for distribution are quite simple -- they don't use any of the advanced features of the software at all. Oh well!