I have a couple of points on this. I agree with what you are saying in principle BUT there are several ways around this.
I have all the tone poets to date (apart from the last 3) and have spent way way less than the rrp for each. I bought the 2lp Cassandra Wilson (which RRP was around the £40) for £18.
@Mr Moore posted a link for it the other day for £15 (from a shop that had multiple copies).
The ones that really hit the wallet are the series that by design are limited (your MM example is a key example here). With those you cant bank on them dropping in value as they will likely sell out. AP's are, from what I have heard, fantastic and I have seen some of them on sale for an affordable amount.
My personal preference is to seek out second hand early/first pressings when I can. A lot of these are hard to beat in terms of audio quality (no matter what the reissue companies try to tell you). I'm pleased with the number of 'classics' in my jazz collection and I rarely pay the average or above (based on discogs) because I'm happy to play the waiting game. As much as it annoys me at times, Ebay plays a big part in my vinyl spending and I have made some unbelievably great purchases over the years on records which should have gone for a lot of lot lot more than what I got it for just by sheer luck (lack of bids, timing of the sale, etc)