What should I expect from ....

a phono preamp upgrade? I am currently running my analog (MMF-5, Denon DL110) through the stock preamp in the Musical Fidelity X150. Mainly real Jazz. My question is- what type of improvement should I expect from a stand-alone pre? My budget is tight. Anything for 500 or less that is worth considering?
My guess is you wouldn't really benefit that much unless your willng to upgrade other componenets. It can be a viscous cycle and very costly and end up never being satisfied. I guess what i am saying is if your pretty happy with what you have let it go and enjoy your current set up....Hope that makes sense..
At your price piont, you might be better off getting a better preamp with built in phono stage--maybe something like an audible illusions M3 or M3A (w/ mm phono stage). Once upon a time, I added a well-regarded 500$ phono stage (monolithic) to a cheap integrated (cambridge a3i). The results were slightly better bass and a cleaner sound, but not really worth 500. Later, I used the phono stage with a conrad johnson pv10al. On a lark, I bought a used audible illusions 2D preamp with built in phono stage. To my ears, it sounded significantly better than the more than twice as expensive monolithic/cj combo.