Fit Progressive springs up front with 15W or 20W oil for a firmer ride. Old springs will have sagged and were a little soft anyway. 10W oil can be used if you prefer lighter damping. To stiffen things up a little try adding 10cc of oil at a time to reduce the air gap. This will increase the effect of the air springing rate.
On the rear standard shocks are fine as long as they are in good nick. People use them for racing on here so they can't be that bad. Better though are Hagon gas shocks, Koni Dial-a-Rides (expensive but worth it - adjustable preload and damping), or Marzochis (a little firm for some people, but the have the benefit of being rebuildable at home). For a Limo ride, sell the wife/husband, re-mortgage the house and get some Progressive 4180 shocks -adjustable damping and spring preload, super lightweight and look gorgeous !
Fit taper roller head race bearing for surer steering, and perhaps a steering damper to iron out any slight speed wobbles or whatever. Get a stiff one up your rear. Ooh err missus! Aftermarket swingers (arms, not sex crazed hippies!) are available in tasty alloy from CMA and Metmachex in the UK. These look the biz and cost the earth £300. Braced ones are even better. Fitting a fork brace (Telefix, Micron or homemade!) will stop forks twisting and walking under braking. This is especially important if you have replaced the stock steel mudguard with a fibreglass one. Other tricks included fitting beefier 20mm axles, but this then takes on more engineering skills, but is worth the effort if you are really determined.