"It's the shape that makes stealth planes hard for radar to detect. Not having any large flat surfaces for the radar to give a simple return off, but to be all angular, so it reflects off in different directions. That's going to make solar panels particularly problematic,"
So hang a large, radar absorbing 'balloon' underneath the bird which deflects energy upwards and away, instead of reflecting. A bit like this handy patent suggests:
"Provide a way to position the solar panels so that they never reflect sunlight earthwards and use a very wide channel for your spread-spectrum comms and it should be invisible to earthly detection."
Low orbit is not very far away, so visual making is as important as RADAR. Anyone with a decent telescope can get some fairly good pictures of spy sats. Some of them are the size of a bus. Photos of some here:
"So we can assume that anything with is easily tracked like the X-37, is probably a decoy or not very important."
They're not far away and not hard to track. You'd be making an incorrect assumption.
Are all these decoys?
X-37 is relatively easily tracked when you have LOS and know where to look. Except it side-steps this issue by being very maneuverable, so you don't know where or when it's going to make an over-pass, making it much harder to counter than something in a typical orbit.