Mr 4 post would benefit from using the search button
Generally most people do the most powaah rewarding PER dollar mods first.
Powah: Extra power from adjusting relative cam angle varies on mods and of course… the cam profile being adjusted. As mentioned, your usually moving the power band up and down the rev range, not "necessarily" making more power.
As such, they're more of a high level tuning tool
Cost: Total cost of mod includes many hours on a dyno with a good tuner to get the most affect from timing changes. (heaven forbid your tuning a SR20 who's gears sit under the cam cover)
As per always, your decision depends on your use for the car. If just throwing a bunch of light mods at it, sell the gears. If your going to be changing cams, turbos etc and want to spend $300 - $500 on dyno time, purely on cam gear adjustment, then keep em.
Use the search button to see the results of others tweaking setups that costly match yours.
PS: Their visual appeal diminishes when you put your timing cover back on... which you'll be doing to prevent a stone from getting under the belt... wont you
Cheers