Hm, you have a point but I think energy drone could still work that way. There are are other items that are much more effective at energy recovery (that sac item especially) and full energy is no "get out of jail card" anyway. Its also not uncommon to not have a safe spot in a room. So what you say only applies to certain rooms and imo ppl would only use it to get back to full if the situation is dire if recovery time of the ability is long enough. Think it would be cool for those situations also to finish of THAT nasty enemy with an energy recovered railgun shot just before you die...
For the healing and support drones its more of a problem though... could be exploited to farm unlimited health/missiles/money. So those could give xx chance to drop an item on room entry.
And two more ideas:
-party drone(!): recolors your bullets to rainbow and has a random drone effect
-mystery deone: low price, random high tier drone but has xx chance to be one of the following:
decoy: just floats around
needle drone: pricks you with a needle on every room entry for 2 dmg
slow drone: slows your own shots when they pass through it