I've seen Mana Eld in RvR and PvE, they are kick ***** I think alot of it has to do with your playstyle. If I rolled an Eld I would personally go mana, especially if your a higher level. The reason you would respec now is because your at 40 and get a free respec. With NF going live I understand that were all getting a skill and RA respec so maybe that will come in handy and if you don't like your new spec you can always either get a respec stone or just use your free respec.
Mana elds are awesome, but like I said I think alot of it has to do with your playstyle. Try copying to Pendragon and trying it out before you respec too :)