the rep life adds up ...
Think 33 rep will be like 3.2 life/second
if the match goes 1 minute that 180+ life
If your oak dies and you rep life, and recast your oak, the life you replenished will be multiplied 2 fold or more
So in a duel that lasts 2-3 minutes, where your oak dies sometimes, could add up to like 500 life
of course rep life is more effective with other character classes, but its still worthwhile on a druid IMO.
I prefer blood boots to get the max rep allowed and use a frw diadem which helps against necros and hammerdins, where sidestepping/running is essential. If you are spear locked vs a necro you can't teleport out