I'm not going to exactly answer the pros and cons of balance shafts or jet valves. A quick Google will get you hundreds of threads on the topic between here and starquestclub alone.

Its a case by case choice. I deleted the shafts as I was doing a supper budget rebuild all without pulling the engine. I found my bearings were in bad shape. Changing them would add expenses, and you can't do it without pulling the engine. Hence my choice. All I'm saying is at the very least pull your shafts out and inspect.

Jet valves are rebuildable and even for sale new. Some guy's like them. Me, budget build. Hence the cheaper option.

88 Montero, StarQuest turbo, Kormex 5speed +tuff-pan w/phoenix f. stage2 clutch, 4in lift+33' tires, 4.875 lsd, short-throw shifter, Aisin hubs, SR big brakes, gen2 uca's, elantra alt, and so much more... 16g turbo w/hardpipes + 4.90 locking disk-brake axle soon (maybe lsd or aussie front??)