Have done a fair bit of leves. Using the cordial potions for the 8 node evaluation ones and stacking up GP before hand as was mentioned. While they are good, in retrospect I would have saved my allowances for tradecraft leves where the HQ bonus is just massive (200% increased xp compared to 25% increased xp for a full evaluation mining one). Stopped doing them at around 40, mostly doing electrum then, I got just about enough of it for my goldsmithing by level 47 (I did however go for HQ crafts/leves, would have gotten away with less mining otherwise, though I'd had to grind more wind shards). Any more leves there and I would have had to backtrack anyway. I'd say just go easy on the leves and use one if you need a jump to a higher tier material for your crafts.

If you're just looking to get 50 as fast as you can to sell top end stuff or whatnot, I'd go full out on the leves though.

Also don't forget your buff food. Even the vendor stuff adds up with 3% xp and a bit of useful stats.

It's a rough grind in any case!