Hello,
just to say that you’ve got few good reply, and here my suggestion along with my point of view.
In my opinion You still too young and you’re curiousity Is far beyond to stay where you are.
Long haul is not easy and depends of the type of Operator...long duties, if Cargo, no cabin crews, sometimes minimum rest, and you will fly from East to West , from Cold to Hot and so on...but in the same time you’ll be able to satisfy your curiousity as long haul flight are completely different from medium haul and you will learn a lot, much more notion and different procedures and a Heavy aircarft. Time for the upgrade depends on the operator, and the hours of longhaul and heavy you got under your belt.
Once you get upgraded be sure you will never go back.
On the other side you have un Upgrade which is always good but if i understood you re not completely satisfied. Then remember an important point, now you’ve got your age from your side later on if you decide to leave after the upgrade you may be stucked there and if you still want to tey the longhaul you’ll have to take again the righ seat with much more white hair.
Think carefully and no matter the money or the left/right seat...do what you feel and like, only in this way you’ll be able to go flying satisfied with an interior peace.
if you ask me, I will go for it( Long haul and Heavy)😉