If you've got leaky calipers I would have thought you'd soon know. It takes very little for the levers to start to feel spongy or low. I would once again put my faith in the Superstars which you're going to order anyway so why not try them first and then if they don't work and you do go down the new calipers route, you will, as you say, have pads come with them anyway. that's before we get into fitting new calipers and how easy it is to spill fluid when you fit and bleed them (presuming using old lines here unless you mean calipers and levers).
I've already bought the calipers, on the basis of getting them at a good price whilst still available, and I can return them free of charge (within 12 months) if I don't use them. The superstar pads are out of stock and have been since mid April. I've emailed them to ask if they're likely to get some in soon, otherwise I'll need to look for an alternative.
I did bleed the brakes during all this as the lever for the rear brake was going right back to the handlebar and the front was spongy too. Fluid from the rear hose was black/grey in colour, while the front was still pink but had a few bubbles. Both returned to full power after bleeding but have begun to deteriorate again. I'm assuming that if air's getting in, fluid's getting out. No sign of any breaks in the hoses but there's much of the rear I can't see as it is routed inside the frame.
My Ice-Tech RT81 discs (6 months old) now have a highly polished, mirror-like finish on the braking surface. Even after sanding them thoroughly, and properly burning in new pads on them, they quickly return to this state. This is why I'm considering fitting new calipers, pads and rotors all at the same time.
