Yah; it's amazing. You get double the normal exp for half the cost! And it doesn't even take 2000 coins to level up a +10 Accessory (any accessory actually) up to half its maximum level. And I don't know if anyone's noticed, but those +10s actually give a lot of stats..........seriously.
That Lv.1 +10 Warrior Ring that gives you 1000 extra attack? That's the equivalent of giving a 5* Knight an extra 30 Lv.ups in their attack stat! Then, spend a little less than 2000 coins to boost that ring up to Lv.20 and now it gives an extra 15 Lv.ups on top of that, a +45 Lv.ups worth of attack stats. +10 Lv.1 Earrings will give an extra +5 Lv.ups worth.
The +10 Lv.1 Bracelet gives +25 Lv.ups and the +10 Lv.1 Necklace a +10 Lv.ups worth in a 5* Knight's defense stats.........buuuuut, the value of this stat isn't anywhere as easy to judge its value, like the Attack stat. Provided that the information on the wiki isn't wrong and the stats of all the pests listed in there are correct, figuring out the value of Defense isn't nearly as easy as adding together 1 + 1.
In a very short summary of the tests I ran, all the way up to Stage 12-5, you can negate all damage taken if your Defense more than doubles the value of the pest's Attack stat. However, it only takes a fraction of your Defense to the Pests' Attack power to reduce their damage by 50% (about 25% Def < Atk). Fortunately for us, all pests appear to only have 75-Defense, so there's no chance of them pulling that BS on us.
Here's a few noteworthy statistics that relate to the value of Defense: