Lack of ideas, then use your imagination when practicing if you are relying on muscle memory. I do it all the time, even the best shredders do this with licks they like. My advice is learn all sorts of songs you like, through that you can deveolpe some interesting variants on what others have done. Either that or learn from some of the runs or ideas they use and build on them in your own works. ALl muscians build off their influences to some degree or another in learning to play you must learn from an agreeable source, play some song you've always wnated to learn.
Malmsteen you could theoretically do by ear if you just memorize the 20 or so licks he uses. Some sweeped arpeggios here, some fast symetrical scale runs here. Not entirely the hardest stuff, but fast.
Learn some Jeff Beck, Jason Becker, Mart Freidman, AL DiMiola...etc....just soemthing to expand your lick arsenal. Otherwise while practicing just get and idea within a scale or whatever and practice it till you have it the way you want it. Don't lmit yourself by saying "I can't play that....or that's too hard..." Because it might seem difficult right now, but it gets easier the more you practice it. As you should know having mastered all sorts of scales and the speed necessary to keep up with a dude like yngwie.