Would there be a problem leaving the washer and or spring in with the Bug ? ... And if so, could I use magnets to bridge the gap so that I don't have to adjust in the cap disc ?
Extra contact points always introduce some resistance, especially if the contact pressure is too low for the interfacing materials.
Magnets / spacers / springs always add resistance that may be significant if the contact areas are too large and too flat, especially if they are not plated with a noble metal.
So, from a performance perspective, it's best to put as few things as possible in series with the battery, otherwise you might need to keep everything squeezed tightly to minimize voltage drop.
From a practical perspective, there is no reason to keep the spring in place when using the Bug, especially in 18500/650 mode.
In 18350 mode, we have found that keeping the spring / washer on the cap when using the Bug compresses the spring quite a lot - so the losses on the Bug are more or less compensated by the added spring compression. Spacers, however, should be avoided at all costs.