When I first read the CB350F maintenance schedule, of interest was to change the oil at 500 miles, then every 3 months or 1500 miles.... filter at double that, and oil pump screen every 12 months or 6000 miles. IF the screen was a big concern, why wasn't it to be cleaned at 500 miles? Anyway, I've never seen a motorcycle oil pan that had any real concern with sludge and certainly not anything that would get into a filter screen.... I think I would do it once sometime after new or after an engine rebuild and after that fergedaboudit.
Opinions will vary on oil changes, but if you're not piling on miles, the only question is does the oil break down with time...... and with no miles, the filter isn't going to be dirty.....