Nice to see another 2310 owner.
I still use a 2310ci and it also has been bullet proof. One thing I will miss is the great connectivity that the 2310 offers, as I still have legacy source components that benefit from its upscaling. New AVRs drop the S-VHS and component inputs unless you move up to some of the higher tier models. Would be nice if the 2310 had pre-outs but the 105W per channel is enough for most and certainly for my listening distance.
I will primarily have 3 reasons for upgrading. One is the move from 1080p to 4k as most TVs are now 4k and 4k content is becoming more common. Number 2 is the addition of E-ARC to the HDMI output which allows the connection of 4k devices to the TV and feeding audio to the AVR. Lastly is the addition of ATMOS as that is the future for surround home theatre.
Having been active on the forums for a couple of years now I will likely stick with Denon. They offer a good balance between cost and features and reliability appears to be as good or better than others. Second choice would probably be Yamaha.