I never found doing dotted rhythms very helpful as a way to speed up fast passages. Lately, though, I've found other rhythms, say long-short-short-short-short, and all the various arrangements (e.g. short-short-short-long-short) to be very helpful. But....it's important to consciously relax completely on the long note, taking however long it takes to be totally relaxed. I find it helpful for a several reasons
First, if I cycle through all the permutations of, for example, one long and four short, then I end up having worked on every possible sequence of four notes at full tempo or above, with a break to relax. I find that makes it much easier to stay relaxed when playing the whole passage at speed.
Second, it's harder than it should be for me to listen carefully to, and remember the sound of a long, fast passage, but it's easy for me to remember how four fast notes sounded - whether they are even, whether hands were aligned perfectly, etc. So it helps me critique myself and see what needs to be worked on.
Third, because of the breaks in flow at the long notes, you cannot go just on muscle memory, so if you want to practice a tricky bit in five rhythms (long-short-short-short-short) in all possible permutations, you really have to burn the passage into your memory, and so it ends up being very securely memorized.