Hi Blowout: The vis display window size was made adjustable for the Bottom Panel in MusicBee versions at or greater than 3.2.6695 (grab the top of the window border); the top of the window bar is also adjustable when the spectrum is used in the Right Sidebar. Be sure you're using the latest version of MusicBee. The FFTScale setting in the spectrum's ini file controls the height (amplitude) of the spectrum bars within the window.
I had some crashing when first setting up the spectrum to my desired look for performance/effects/size, but since then it's been completely stable for me. Of course, this could be locally affected by what other plugins are in use, skin, OS, etc. I'm glad you got your size issue resolved. If you have any more questions, feel free to post and I (and others) will try to help. I love this spectrum!