I like the idea of having an assortment of visa and path to citizenship options, so the possibility of stricter EU enforcement cascading to other members worries me (a little).
On the other hand, the impact of some of these programs on housing markets does seem to be real. In all likelihood, the impact is negligible compared to AirBNB or similar, but "ghost properties" seem to be real issues in places like London or Vancouver where housing stock is tied up by folks who used it to gain access to a place but don't turn around and use it or rent it. Not sure if the Malta plan was inclusive of real estate or not, so may not be a relevant worry.
This was good to read, though: "Current EU legislation does not, however, regulate conditions for granting residence permits, which several member states offer in return for investments."