Kind of depends on how you think and hear music. Can you hear/sing what you would play? If not, then you're playing mechanically. Doing exercises that replace one mechanical device with another isn't improvising, it's just another form of painting/playing by the numbers. If you want to be able to play what you'd like to hear then this requires becoming "one with your instrument". There are lots of ways to do this and some achieve this via mechanical means, but that can be a long way around (check out other similar posts for more info).
If all you can hear in your head are blues scales, then it's like saying your sick of eating hamburgers. What's the solution? Stop eating hamburgers! Listen to, and get into, other types of music. Transcribe (preferably by ear) and incorporate whatever you like and try to sing whatever phrases/melodic lines you want to play. If you can't hear them in your head, don't expect much to come out of your fingers. You still need to have technical skills (be able to play in all keys) with some dexterity.
The mistake to be avoided (IMHO) is to approach everything as though it can be fixed by a mechanical prescription. Improvisation, if it's good, always comes from within. This requires ears that are trained as much or more than fingers and your instrument becoming your voice. Seems obvious that one can't sing if you can't hear in your head what you intend to sing. Same is true for improvising convincingly with an instrument.
