If you have a UK PPLH with several type ratings on it then you have to do an annual LPC test each year on each machine to remain current,
Not strictly true. Single engine piston helicopters all require a type rating and two hours a year must be flown in each type but the LPC need only be done on one of those types, not all of them.
By all means do your FAA PPL(H). I chose not to because I eventually wish to fly commercially in the UK and an FAA ATPL(H) would make that a bit tricky!
Personally I don't mind being checked out once a year as I enjoy having my wrists slapped by my examiner for all the bad habits that I've got into (in a year!!) and it forces me to revise and practice emergency procedures - a good thing in my mind. The marginal cost of the examiner's time is really only a few quid on top of the hire of the machine itself.
Cheers
Whirls