Once you get to modern day Deore level, you'll be good to go. That's more than most will need/want. I'm running XT FD/RD and XTR shifters. It shifts like butter. But, that's not the whole story. The cassette does make a difference and so do the chainrings. The higher up the line you go, the better the ramping becomes on those components. It'll allow the chain to move up and down the gears easier. Then there is the chain. Cheapo chains will work just fine, but the better the chain, then the better the shifts...and perhaps less noise.

I run a SRAM Powerglide (spider) cassette, XTR/DuraAce chain. My current setup shifts very smoothly and if you hate noise like I do, then this kind of setup will do quite nicely.

I'll add that on my partner's Trek FX 7.4, it has a mix of Alivio and Deore components along with the stock all steel cassette and a KMC X9 chain. It shifts ok but it's a noisy setup. Riding my bike back to back with his and you can tell the difference. However, if you never get on a bike with higher end components, you may never know the difference.

Doing a quick search on the RD. An alivio would cost you ~$18 on ebay. A deore would cost ~$40 - $50. But you add up all the parts and it turns into some real dough. My suggestion? Go ride a few bikes with lower end components then ride one with higher end components and see if you can tell. You may or may not be able to. My partner has done a test ride on mine after riding his and he tells me that he can tell a slight difference, but it's not worth it to him to upgrade his parts.

On my MTB, I have a frankenstein setup wth Sram XO and XTR mix and match. It works great. I can tell that it shifts smoother than my XT stuff. But the step from XT to XTR is pretty big.