The fact of the matter is that it wasn't for "manufactured on demand" most of those classic films would never have seen a release on DVD. Demand for those titles just isn't enough to support a full-blown retail store release. Warner Bros. found a way to make them available in smaller numbers while still being profitable and other studios have followed. Obviously it's become a big success for the studios and collectors alike.
True, in the early days, there were problems with some DVD-R releases, but over the years quality control has improved and frankly the format has received an undeserved bad rap. Nowadays, most of the complaints seem to come from people who have only "heard" that they're troublesome and have never bought any themselves.
Speaking for myself, I have about three thousand DVR-R discs that were recorded over the years and have yet to have a single one turn into a "coaster".
In a way, it is too bad one can't wander the stores browsing at them, but if comes down to MOD being the only way to get access to those otherwise unavailable titles, I'll gladly forgo browsing.
Outside of TCM actually playing them, this is really the way to go for many of the harder to find movies.
I have about half as many DVDs as you, but also do HD recording as well. I suspect that the DVDs that turn out to be coasters for other people were coasters to begin with, and weren't detected (as they might if they had used Verify with ImgBurn). That is not possible with a shelf-top unit though, unless it temporarily stores the video on a hard drive first.
I have read the results for a study or two that show the outside areas (normally unused areas) of a DVD not holding up, or otherwise failing after torture tests, but that is torture testing and not using the DVD as designed. So I think we can safely ignore those too.
The following is for others, in case they might be having issues:
As far as earlier first-generation stamped (replicated) DVDs not holding up, that is very well documented, as the layers were separating at the glue. This can be observed as spots or splotches on the media side of the disc. Things have changed significantly though since DVD technology in the early 2000s, and I haven't had that happen since.
Vast improvements have been made for burned (duplicated) DVDRs as well. The brands I use are Taiyo Yuden, and to a greater extent, Verbatim AZO (AZO is a marking on the container, not all Verbatims have this). The non-AZO Verbatim discs are made in a non-Verbatim facility in China.
Manufacturer can be verified by putting the DVDR discs into a computer and running the freeware program DVD Identifier, which will read the manufacturer identification number on the DVDR disc itself, and give you the actual factory of origin.
So for instance the Verbatim AZO series (and also the DVD-R/W discs) will say something like "MCC (Mitsubishi Chemical Corp)" or "MKM (Mitsubishi Kagaku Media)", whereas the non-AZO series will say something completely different. FWIW, I tried a couple MOD discs just now, and presumably due to the copyright protection, I was unable to enumerate the manufacturer on the first try.