Agree 100%, I did/do about 18 second hills, and then i have a couple minute jog/walk in between...the session takes 40 minutes or so; you have to be patient so that you dont build up lactic acid. Also, this way you can fit this session into your normal strength regimen without completely exhausting your system....just soreness for microtearing the fast twitch muscles, which you can run mileage on.
Do not slow down. Do not decrease the slope. The point of these hill repeats is to clean up your stride and improve knee lift. A little bit of lactate is ok, but you do not want anything near that feeling you get at the end of an 800m track session. ie 3X3X300 or 4X400 or 12X200 with short rec etc. So shorten them. 30 seconds is a bit too long. 4 seconds would seem too short for practical purposes, unless you did about 100 of them. Somewhere between 12-18 seconds sounds good. I do 15 seconds, although I do not time them.
Soreness is not caused by lactic acid. It is caused by microtears in the muscles. That is why lifting weights causes soreness, as does downhill running.
One thing that I do when I am starting to feel the head spinning is to not focus on turnover--just explode through each stride and exaggerate the back kick on the hill (otherwise it gets cut off) to work the glut and upper hamstring--you are "bounding" more and it feels like a weight room workout, but with the perfect dynamics of running.
I can tell for an older runner who is experimenting on myself, the power training is something you have to focus on. My stride length/explosive power sucks right now...