I would say it depends on many factors .In general you could say overupgrades don't worth the effort, however if you aim for a certain def/reduction value it might be worth it and that on the other hand depends on how much def you already have.
Since most equip has a low base def value compared to later equip upgraded contribute more to reduction, still the effort is hardly worth it unless you aim for specific gears that benefit from cards (like garmet, shoes, headgear) if they are upgraded to +9 (bonewand might be worth it to +10 if/when skull cap hits the server).
Beside that .. its just for the hell of it and the hope to get a hugh load of money by overupping gear that is easy to obtain (like coat).
If that isnt reason enough there is still the one reason that always works : Why the hell not?
Coat is cheap, tons of elu and enriched elu are not. Also, as the title suggests, I am specifically talking about armor and shields. Anything else has an obvious factor of why +7 and up, especially weapons. Again, we cannot talk about anything other than +10 armors and shields in current RO since everything else has a good reason to +9 at least.
Also if you had extra zeny, wouldn't it be more beneficial to buy kafra items from people such as Silvervines? I mean it seems a lot more productive to have those than to have a +10 coat or +10 buckler lol. Remember the guy with a +10 Pantie [1] that ended up selling it to the NPC because nobody could buy it at the price expected? I'd assume it's because +10 items aren't as worth as much as the risk. So unless you're super lucky and made it out of random curiosity of pushing Upgrade>Upgrade>Upgrade and miraculously made it to +10, it seems like a net loss over all.
I suppose you're right on the if you have SO much zeny and don't know what to do with it, then the zeny loss wouldn't matter to some people and they end up doing that lol.
Edited by Quoc, 23 September 2017 - 11:25 AM.