That's a pretty subjective question. If you're looking for opinions, I'll give you mine for what it's worth...
I definitely like gaming mice. I recently upgraded from a cheap one to a Logitech G500 and wish I'd done it years ago. It feels much nicer, slides much more consistently and the adjustable dpi is handy.
I got a keyboard a couple of years ago. Again, I subjectively like the feel of it much more, though unlike the mouse I can't say it's helped my gaming at all. I imagine if you're an MMO player or are into programming macros, the additional keys offered on some keyboards could make a massive difference. That's not me. I do a looooot of typing however, and the mechanical keys are great (again - subjective!). While at first I wondered whether I'd wasted some cash on the keyboard, I've already got several years out of it and expect it to last many hundreds of hours worth of typing yet, so for me it's a good investment.
Personally I think it's a little strange when people sink big $$s into a gaming rig and then skimp out on the components they actually interact with (keyboard, mouse, screens). But others would see it differently. I suppose my only suggestion would be to try one out, use a friend's or go to a shop, and see if you like it. Decide whether it's worth it for you.