Is my interval training routine effective for mountain bike training?
Whether an interval training is effective or not depends mostly on your particulars relative to the interval. Heart rate is only a very inexact measure of effort, but you seem to be roughly in the ballpark. However, such quick switching between on/off interval state does not generally produce interval-like results and should be viewed as a single 30-minute interval at the average power of this period. 

A better gauge of interval quality would be this: how long can you keep up the effort? A more typical interval training might be e.g. 6-7 times 3-8 minute efforts, with 2-5 minute rests, at such intensity that you simply cannot complete another interval round.

A goal of "strength and speed" on the mountain is unspecific enough that you can be sure it's being helped somewhat, and in some way, by the intervals. However, it's counterproductive to do interval training and weight training both in one session. If you are still in shape to do weight training after your intervals, it means the intervals weren't done hard enough. Do intervals and weights on alternate days.