There are lots of good comments on this thread, and I hope they help. I've been vaping now going on 2 years, and I ONLY vape ONE flavor. All day, every day. Have since time out of mind. I smoked menthol cigarettes over 40 years. Now I vape menthol. That's it. So it's not "boredom" when my taste goes wonky. There are lots of factors involved. If you want to switch flavors, that's fine. But you don't really "have" to...because while it might help,that's not really what is going on.
Pretty much the same with the delivery devices...whether the thing that holds the juice itself or the thing that has the power to heat up the juice in the thing that's holding it. Get the best quality you can manage, and if variable voltage is useful to you due to changing flavors a lot...that's great. But there is no magic bullet what voltage is "best" for everyone. And there is no magic bullet what juice holder device is right, or what ohm it has that is "best" for all.
It sounds like you hit on something that you found really enjoyable. The sudden change where the flavor was "gone" can be due to lots of factors that have NOTHING to do with the device or the juice you are using. Stress. Hunger. Being tired. A very strong flavor you just ate. A headache, or other body aches. Anger. Depression. Tension. Thirst (recognized or not). Cigarette taste has the same phenomenon as the PV. The difference was that one knew that the cigarette they had was, well...what it was. There was no expectations that it could be improved upon by purchasing some other version. Yes...you could change brands. But, be honest...did you really change brands daily? Or weekly? No. You just smoked on a brand for however long, no matter that sometimes it didn't taste that great. When the price went up, or you just felt like you wanted to try another brand, THEN you might change. Otherwise...you smoked what you had and didn't think about it. With vaping you know there are options. Therein is the temptation to fall into "searching for the perfect vape". It's one thing to have a hobby. It's another thing to keep buying things because you might think the next thing might be the solution to the periodic doldrums your tastebuds may be suffering.
I have found a delivery system/s that works for me. But I don't expect it to always taste exactly the same every time, even though my juice is exactly the same, and the device is exactly the same. The reason I like my bottom feeders is the long battery life, and I can carry between 4 and 9 ml. of juice with me in a compact package and vape without worry for many hours...or a whole day. But..yes. During any given day things will taste "off". Or hardly taste at all. Or seem too harsh. Or something. And when I stop and think about it...I can usually pinpoint was is REALLY going on. I'm tired. Or hungry. Or ticked off at my husband. Or worried. Something. It will pass. Taking a little break from vaping (a nap, or a shower, something to eat, or a run around the block) will usually jog things back in working order again.
For really bad cases...a 1/4 teaspoon of baking soda mixed into about 6oz. of water. Rinse the water/soda mix in your mouth and spit. Repeat until it's gone (don't drink it!) That can help clear your tastebuds again.