I've been a 1K for years, and Plat is a new level I've never had, so I have to tell you my experiences as a 1K.
One significant benefit is elimination of almost all fees. Being able to redeem and redeposit awards without fees is very valuable to me. I don't believe Plats get this but I don't think so.
Second, you get a lot of upgrades. You will get a pair of CR1's at 75K, but at 1K you'd get another pair of CR1's AND six SWUs. If you don't travel internationally, they are worth a bit less to you (unless you exchange them in the CC). For me, they are very well worth it. I look for flights have have upgrade ability the day I purchase. Even the few times I haven't been able to do that, they have almost always cleared. Not 100% of the time, but more than 90%.
Anyway, just my input.
Billy