Unless you really want a console exclusive title and are willing to buy a PS4 for it, go ahead. Anything less, upgrade your PC. A PC is getting a longer and longer lifespan. And you can buy a rather hefty piece of videocard for the price of a PS4, keep in mind that you DON'T need to buy a $1900 Alienware gaming rig, I actually would advise against that ;-)
One of the advantages with a PC is that you can get great deals for PC games over at Steam, Humble Bundle, GoG, etc. Much deeper discounts then for consoles, which eventually saves you money, a lot of money over the lifetime of a console. And you can generally keep playing your games for a long time on newer hardware, for older titles you need generally older consoles...
I've been running the same quad core CPU (Q6600) for 7+ years, for 5+ of those years it has run 16hrs/day, 7days/week. The same videocard (GTX285) for ~5.5 years. As you can see, you can do a long, long time with PC hardware, most consoles won't stand up to this kind of (ab)use...