What gear should I be targeting as a Druid approaching lvl 40?
 

I have just been trying to get any WIS pieces I can as I'm leveling, but I wanted to know if there are items that are integral to Druid solo leveling later on that I should try and buy.

I have seen luminescent staff mentioned before in other threads, is that worth a buy for the free lightning strike? Any other must-buy recommendations? I pretty much play solo always, for what it's worth.

If you intend to quad, lumi staff.
If you intend to charm, goblin ring.
If you intend to group, any clickies (Tunare necklace, elder spiritist gear, etc.) and then a good balance of mana/hp (for when you get aggro or aoe'd).

That would be my suggestions. JBoots is good for anyone but a shaman.

Lumi staff is good for quadding but not clickable until level 46.

As a druid who just hit 46 I can tell you that elder spiritist arms at 45 was a huge help while quadding. Use them to finish off mobs or if I got a 5th add by mistake I just kept the extra mob dotted and finished it off after the kite. Huge help instead of trying to sit every 6 seconds.