The spellstrike set is only two pieces, so if you're going to invest the time into making one, I would definitely make the other. With both pieces, you'll not only improve your hit rating and damage more, but you get a set bonus as well. I've heard that the bonus procs decently, but even if it doesn't the extra hit rating is worth it, imho.
Of course if you have a piece that out-does one or the other of the set, stick with it if the only thing you'll improve is the "chance" to deal more damage.
I can sympathize with all the farming you'll have to do, I need so many primals for all the sets my clothies will need it makes my head spin. But I think it'll be well worth it!