My take on the great rock and blues improvisors is that they all have an enormous musical vocabulary. This means they have amassed enough musical experience (read: PRACTICE!) to be able to go to the well over and over without becoming stale mid-solo. You can easily tell when a player has exhausted their musical vocabulary, as they tend to resort to cheesy tricks and noise making (read: wailing on the trem-bar for 48 mind-numbing measures)
My advice would be to always force yourself outside your comfort zone - learn new riffs, phrases and scales. Incorporate them into your vocabulary. Practice breaking out of the pentatonic box - there are dozens of notes "inside" that box that will sound great if you use them.
Lastly, try slowing down and drawing out the energy with some sustained whole notes with vibrato, or perhaps some awesome complementary chord progressions amongst the single-note runs. A great solo does NOT always have to be about speed and flash. (David Gilmour anyone?)