I think DDMs are suffering from two things (beyond the random distribution, which has been a "problem" since the beginning):
1) The quality of the sculpts/paint jobs has declined. Some examples are worse than others but we're seeing an increasing number of simply bad, bad, bad paint jobs (and it's not just for commons).
2) Saturation. When you're getting the sixth or seventh (or whatever) bugbear sculpt, you know they're running out of ideas. I have probably close to 3,000 minis now (the bulk of them duplicates) and I've noticed that I'm being more selective in what I buy on the secondary market (I rarely buy primary). And when I do buy something that I've probably already got covered, I buy less of them. I've been tracking the number of minis I've been buying by set and it's been in decline for the past 4-5 sets. The decline has plateaued but I'm simply not buying as much as I used to because I've got most of the bases covered.
Solutions? I think they should put out maybe one less set per year to increase anticipation, put greater emphasis on quality control, and do a better job of polling the audience to see what minis we're looking for. There's also the non-random mini option but I don't think they're going to go there.