1. well worth it
As you get faster, you'll need to use more braking power. As you brake harder, your front forks will travel alot further (vertically as they comrpess). I suggest using Racetech's "Spring Rate Search" calculator to discover your recommended front and rear suspension suggestions (https://racetech.com/VehicleSearch). My 07 ZX6R stock front fork springs is .87KG/MM, so i ordered a set at .90KG/MM and am loving it. For street riding, since this is a stiffer spring, the suspension will reflect a stiffer feeling. Not too bad really, but very noticeable on track in a positive way. Dialed in suspension (to your height/weight/riding style) and good tires should be prioritized when it comes to first upgrades/"mods" and is the best initial investment in yourself. Again, i recommend these springs and suggest using the spring rate calc.