Depending on which 2407WFP you have (the -HC and later the 2408 have slower panels) you could potentially benefit from a modern display with lower input lag & higher refresh rate if FPS gaming is your thing. That said the Dell is very well built, its clearly not unusual for them to keep running just fine for 10+ years & I've never had any real issues using it as a display. I'm not sure the same is true of many of the displays your could be tempted to replace it with unless you spend a similar £400-600 as the Dell did back in the day. The other issue is aspect ratio, displays have mostly (there are still a few 16:10 around) moved to 16:9 so if you valued those 1200 vertical pixels you may have to move up to at least 1440.
Personally I think 4K is excessive on anything much smaller than 40", not everyone will agree but until all software starts to properly implement the kind of scaling we take for granted on our 4K mobiles there will be the odd app that looks horrendous if you enable scaling in your display settings. However 4K displays are perhaps less of an issue than many make out for gaming, plenty of people here either make a custom ultrawide res with 1:1 pixel mapping that a 980/1070/1080 can handle fairly easily &/or just turn down some of the hardcore options that make very little visible difference.
You could do worse than go for something like an Omen 32, its bigger than your Dell with a suitable increase in resolution while presumably being similarly well built, downside it's not GSYNC compatible to match the capabilities of your card, but if you've been running 60Hz vsync for the last 10- years maybe you don't care.
Most the big/curved displays seem to require a compromise of some sorts hence several threads on here bemoaning monitor quality and the fussy DSR abusing little ***** who keep sending units back until they get something they consider acceptable.
