I split this thread out into a separate document (I may later move it too)... as it's gone way OT for the original thread, but deserves discussing in its own right.
First up - money. I don't intend to monetise this in any way. I see this is a resource for members - and, possibly, block it to members who have posted less than "N" posts and/or been members for less than "X" days/weeks... or maybe not, after all, it might well be a draw for new members as Bob said.
Second - ideally, it'll be handled through the forum itself, if there's a suitable plug-in for SMF. If not, then something that can be hosted alongside the site would make the most sense.
Third - format. Yeah, PDF for the full manuals without question. However, if I can round up any volunteers, who would be happy to pick the PDFs apart, then I'm thinking a Wiki-style site (which is indexable and searchable), certainly for more popular manuals might be worth a shout. However, if there's one thing that's certain, there's no way I can find the time to look after such a thing! So definitely need volunteers for that one. The other thing a Wiki gives us, is the possibility to create our own manuals - e.g. where original information is unobtainum; or as a result of hard-won experience (I'm looking at you Listeroid boys in particular here). How useful would that be? Again, with suitable volunteers, I'd say we pick apart the "wall of knowledge" forum (which is not well used, and not user friendly IMHO), but also the sub-threads that appear in various other forums, some going back 10 years or more, and convert that knowledge into article form. I reckon that'd really start bringing people in. Again, I'd tie access into the forum, so you have to be a member to view the wiki. Think Wikipedia, but on a way WAY smaller scale!
As far as cash is concerned - fear not! This, and one other, forum co-exist on the same server, in a data centre in London (IIRC), which costs me around about US$25/month including full daily backups. So I'm really not worried about funding. I think we (and the other forum, and all the other gubbins I run on the server) uses about 2% of our monthly bandwidth limit as well, so we've got some room for growth too! In fact, the biggest hassle is disk space; and I should have that solved soon, we're eligible for a free upgrade which will make the server faster, and double the disk space available to us. Plus I can always buy add-on disk space for a few bucks a month.
VP - the Peter & Rita Forbes site is an interesting one - it was a lifelong passion of Peter's, but the site itself is a very "traditional" style HTML based site (of the mid 1990s style). Extremely compatible with any old device, but also a pain in the arse to maintain. Unfortunately, now that Peter has passed away, it's unlikely it'll ever be updated again. I presume Rita now owns it, but since the Stationary Engine Forum effectively disappeared after he died (he was the driving force behind that forum), I can't imagine his website will survive for many more years.
And, since I'm rambling... I suppose Bob, Andrew and I should sit down and work out what we do if, god forbid, any of us kick the proverbial bucket... I think all three of us are currently essential to the ongoing survival of this forum, so it's something I'll try to get sorted with the chaps for the future. Although frankly, I intend to live forever (just not necessarily on this planet), so we shouldn't have too much to worry about yet!