The ones w/o die-cuts that have appreciated thus far are few and far between, about a handful out of maybe 100 in total. And it's not the press sheet per se as very few collect these, it's usually panes/booklets or pairs. Popular subjects, nice designs AND low print quantities help for sure. Something that only appeals to a small percentage of collectors, usually the politically correct issues, don't. Take the Eid press sheet issued in Aug 2013 for example - 500 printed (back then the norm was 2500) - and it's still available:
https://store.usps.com/store/browse...p-collectorsHarry Potter, Inverted Jenny, Made in America, Modern Art in America, Vintage Circus Posters sold out almost instantaneously because these appeal to a wider audience.
These are the ones worth focusing on imho, but that requires a bit of luck sometimes as you cannot necessarily guess the taste of the masses... But let's say there will be an Elvis Music Legends PS with only 500 available, go for it!
The problem is that there are too many new press sheets being issued and that the average collector just doesn't have the money to collect both perf and imperf issues. And why would you? Most collect because they want one of each design and very few, hardcore collectors want everything.
Just look at
ebay what kind of year sets sell - usually the cheap ones with half of the stamps missing, mostly definitives because these are often ugly.