HW heater ? Don't have one. Never have, so not a necessity for us. We get by with the stove, kettle/large pot, facecloth and tub method, or preferably, bucket and scoop. Better still, swimming.
Do you wish you had one ? Not really. Definitely agree a shower is nice thing but we have no means to "shower" onboard, no shower head, plumbed water system, pump or pressure. We do have a privacy tent but what I'd really like for "next time" is a dedicated wet room inside the camper. Then we'd prob continue with the bucket and scoop method for simplicity.
Refrain from showering while boondocking ? No. In fact we find it easier to freshen up or wash the hermit beard when in the bush with the absence of other people around. We carry a lot of water - too much I've read on this site but nevermind. I'd turn the question a bit and ask, do you shower when there are facilities available, eg in a CG. We don't choose to use CGs because of showers but we'll usually use them if they are on site. Going forward with covid etc who knows how we'd use such facilities ...