First off, are you sure they aren't JLWs?
If you've managed to graft a servostick restrictor and servo on JLFs, I'd like to see pics.
If they are JLF's, paradise arcade shop sells springs in various strengths.
IMO, the 6lb ones feel like the old beat 'em up sticks, but it may be a bit too heavy.
Order a selection ranging from 3-6lb and compare them.
Lube the crap out of everything (with super lube) or else they'll feel "notchy", like they move easily at first then require more force to get over a hump.
With the plastic bat tops and stiffer springs, they'll feel more like Happ/IL, but smaller.
Either way, the springs are what you want to change to get rid of the "dainty" feel (I used the same word to describe my JLFs when I first got them).
Changing switches is more about getting rid of noise.
If they are the JLW's, I think Ultimarc offers a stiffer spring (for their rebranded JLW), but not a variety of weights.
Here are my opinions on the stuff I've tried with JLFs:
http://forum.arcadecontrols.com/index.php/topic,135398.msg1398302.html#msg1398302