I think Disney's overall approach to direct sales right now is going to affect monorail (and other resort) resale prices. The recent BLT incentives, the influx of VGF points that look a lot like poly points (easy access to the park, but too many studios), and also Poly points are starting to enter that magic 7-10 year post resort opening range where original owners who may have bought with young families are going to be phasing out of
DVC making supply of points increase.
Not sure any of this is going to like, tank resale prices or anything, but if you have a personal reason to want VGF (blue card, or maybe you always wanted VGF, but were only buying when poly was active), this is as good a chance as you might get to "convert" your home resort. The incremental increases in Poly contract value over time aren't likely going to outweigh the relative direct price for VGF, if you really want it.
Another way to look at it (as I think you presented it), you seem to have interest in some combo of VGF being preferred over poly and also somewhat like the idea of getting a blue card. the difference between average poly prices (per the board sponsor) after the commission/fees are probably in the 160s right now, and a 200/300 point contract at VGF is going to be priced around 179-186pp after incentives. is this "upgrade" to your membership worth approx. $20-25 per point (I dont know how big the contract your selling is).