Go with some rugged pro-sound equipment. Keep it simple with a pair of powered PA speakers. They will easily fill the room with clear sound and are built to withstand frequent setup and breakdown. Check the pro-sound area in partsexpress.com.
The difference is very content dependent. Some movies like the Star Wars releases of recent years are actually coded for it and certain stuff like flyovers seem to benefit, but the improvement is subtle.
I would think that if you had speakers with excellent bass and mids, but the highs, not so much, those tweeters might be just the ticket. Also, they could be worth a risk-free try for 30 days, risking only the shipping charge which can't be too high because they are small.
An excellent, clean-sounding sub for music with plenty of output in the 25hz and higher region is the new SB12 Plus. It is a little more than $500 however.