I think the "gap" between Gold and Platinum is as small as its ever been. 5 years ago, PM was a big deal, now -- not so much.
Why?
1). Domestic upgrades are now "free" for everyone.
2). Domestic upgrade sucess rate is about the same (for me, at least).
3). PMU's in the late '90s could be used with relative ease of Swissair, Sabena, Finnair (SFO-HEL codeshare) and AF. Now, it's much tougher, and we only have AF to work with.
4). Discount business class fares are competitve with YBM upgradeable fares internationally, and you get double MQM's. This also devalues PMUs.