Personally, I would. I think the price rise is a legitimate concern as PE is priced far, far below both cost and the TTM market price. Fares will probably stay low longer than I expect, but it is a real risk.
A PE fare has priority over all Economy fares (any status except GS) when it comes to upgrades. However, the biggest reason in my mind to buy the R fare is that if you don't succeed at the GPU, you at least travel in a reasonable class of service. If the upgrade seems a sure thing, then don't pay extra. PE does not include lounge access of any kind (though of course your *G does).