Assuming it really is a 2010, I think it's worth trying an SSD upgrade, but don't throw money at an expensive (OWC / Samsung) SSD. Buy an el cheapo SATA SSD: Mushkin, Adata, Toshiba, a few others are often available for quite a bit less than the Samsung EVO's. It's not too hard to get into the older iMacs, you just need to work carefully and without interruption.
Replacing the original HDD on our early 2009 iMac with a Mushkin SSD made a significant difference, and I expect we'll keep it for another year or so before replacing it. Before the SSD upgrade, it was getting really annoying.