Two words, vacuum pump! Speed bleeders also help. Don't forget one front brake is the front lever, the other one is the rear pedal!
Delinking is a debate for sure! Personally I like the linked brakes better for the most part, and delinking won't do as thing for the front lever! Removing the anti dive will give more power to the front brake but then the bike will tend to nose dive when braking. This too is a hot topic and I personally like the anti dives.
OK now to the meat and potatoes. If your front lever is spongy, this can be due to two or three things. First, the master cylinder needs rebuilding. Your seals in the master cylinder are most likely experiencing blow by from worn seals, corrosion on the cylinder walls, or both. There are rebuild kits out there that are inexpensive but I also recommend honing the cylinder wall, or replacing the whole master if the walls have major pitting. Secondly, your caliper may have the same issue as the master, same things apply. Now lastly, your rubber lines are 30 years old, most likely!! Replace them before they blow out!! Replace them with stainless steel braided lines. Rubber expands robbing power to the caliper, even when new. The SS braided ones resist this expansion and provide more working power to the front.
Other possible causes of spongy lever are somebody loosened a brake line and did not replace the crush washer! Even though there may not be a visible leak you could loose a certain amount of pressure from weeping. Also crush washers can develop corrosion thru the years and loose a small amount of seal. When you replace your brake lines, including the ones to your anti dives, use new crush washers. Speaking of the anti dives, yes I suppose it is possible you have an internal leak in them. Your best bet, find front forks off of a MK2 along with rotors, and put better 4 piston calipers from a Yami R1 or R6 and be prepared for some real stopping power! The electric solenoid anti dives are powered via the brake lights...