Ask yourself: Do your PVP/Boss encounters last 60 seconds or more sometimes? Do you take damage in the first 10 - 20 seconds of these encounters? Would you like 400 - 500 more HP during those encounters? Are you willing to forgo using a green blossom or other body buff for the possibility of having said extra HP? If you answered yes then Replenishment is the pre-buff for you!
To clarify Replenishment regenerates 10 HP/sec for 60 seconds. So if you're at full HP when you cast it you're not getting any benefit until you take damage. As I said earlier though, if you take damage in the first 10 - 20 seconds after casting Replenishment you're looking at 400 - 500 HP regained for the rest of the spell's duration. That is if you survive that long.
For PVE it's usually easy enough to just back off and sip some Sunny-D, so not that useful. For PVP on the other hand healing is either not an option (frowned upon in duels) or risky (in other encounters), so Replenishment shines as a way to boost your total HP beyond what is possible by other means. It can end up being useless in some encounters, and you may have to adjust your play-style to take advantage of it's benefits. For example trying to trade hits with your enemy early on, then playing more passively, unless your HP gets topped off then going aggressive again.
Greater Magic Barrier is a viable alternative. If your opponent doesn't have any ability to deal magic damage though, you've wasted a spell slot. Other than that pretty much WoG. Force can be used to stun if you don't want to go into another NG+ to get another copy of WoG, or if you simply wish to save your WoG casts for the time being. Attuning another copy of WoG is usually a better use of the spell slot if you have the option though. Emit Force is slow to cast and therefore easily dodged, but it can be useful in narrow corridors and such. Then there's the Sword Dances which I mentioned earlier in the thread.