That is the dilemma, isn't it?
If you only attack Israel and US assets in the region, that amounts to not much because, at the end of the day, they can withstand more than Iran can deal with. Especially the US, as it was untouched by this, you may destroy a few bases here and there, but it's not something they can't rebuild.
Spreading it out and hitting everyone, which is what the Iranian doing now, would mean you spread out the damage, the area increase as the intensity decrease, because you only have a finite amount of missile and drone and if you have more target to hit, that may or may not have any direct impact on the war, that mean the damage intensity is spreading out.
So if Iran wants to win, it can't win by attacking everyone, because that will be like Nazi Germany bombing civilian targets in London instead of military targets. The US and Israel would be glad if Iran kept on doing what it is doing. After all, the damage was shared equally; it didn't hurt them that much. On the other hand, if Iran focuses on US and Israel asset in the area, can they really set the American and IDF back? Very likely to be a no, in fact, it will open Iran more on the attack, remember the majority of the stuff the US sent is with 5th Fleet, now anchor outside Israel at the Mediterranean, but that's not the only US asset in the area, Diego Garcia was not use (as the UK not allowing them to) and the 3rd Fleet and 6th Fleet was not used. No US assets are coming from the South into the Strait of Hormuz, so it would not be good if Iran focuses on all the targets going North.
On the other hand, I don't think Trump care about American casualties at all......
