Allow multiple boosting rates
I checked the list and don't think I saw this anywhere. But has anyone ever suggested different boosting rates? As an example, at my heroes current level I can train 2 full raids from the barracks in the time it takes the heroes to fully recover. But the only boosting option is 4 times recovery rate. Which means if I boost half the time my heroes will be standing around waiting for troops to finish. This obviously varies with the level/heal time of the hero. That's further to my point though, since we all have different level heroes and different troop raid makeup, it would make sense to have multiple rates of boosting with corresponding gem costs to accommodate different needs. To anticipate a rebuttal, to those that would say "boost barracks as well", barracks boosting also is only offered at one rate ... the same rate heroes boosting is. So boosting barracks would leave me in the same position I was in before I boosted: 2 full raid armies in the time of 1 full hero recovery.
Now, I know what you SC folks are thinking ... "We want you to pay more gems than necessary ... that's how we can pay our employees". But think about the possibilities. You could also offer higher rates for people to use more gems. For example ... I want to boost my lvl 6 drills at 4 times the rate instead of 2. Normally it's 30 gems a drill. If I wanted to boost it 4 times though charge exponentially more ... like 300 gems. I'm sure you have experts at in-game currency balancing, but just using the example to highlight the possibilities.
Just to recap in case the above is too obtuse:
Request multiple boosting rates, i.e.
Reduce hero heal time x 2 for 2 hours: 5 gems
Reduce hero heal time x 4 for 2 hours: 10 gems
Reduce hero heal time x 8 for 2 hours: 50 gems