......whether expensive dies aid accuracy or not?
Just buy locking collars, if you use single press then the dies are always set up correctly.Lee dies are fine once set up but if you are changing them between loading sessions then they are a bit of a pain to set up each time.
I find the exact opposite... I have Lee Classic Cast and there' some similar size Lyman press at the club (that I never use). Lyman is supposedly "cam over" design but it has so much play / compression that it doesn't give repeatable results. Classic Cast is on par or better with just about any US press (Präzipress etc. are in a league of their own).I also found with my basing Lee single stage press that depending how much pressure I applied to the arm would alter the seating depth of a bullet so it was very difficult to achieve consistency. With the Lyman press I have there are no such issues.
I find the opposite. I never worry about trying different bullets and jump lengths when using high quality dies along with a micrometre just keep dummy rounds of what works, wind down onto your dummy and start putting the next batch together . Want to try nearer the rifling turn 2 tho' longer and try a fewExpensive/good dies… improved accuracy is dependent very much on how you set them up & use them.
Using bog standard set up of the resizing die won’t improve your results much (If at all) but will probably give you less hassle.