My home has an older (late 60's) General Electric 100A load center. It has 16 spaces. All are taken. In the panel there's a 30A 2-pole breaker feeding a 4 space sub panel, which is full as well.

The house (built in early 1800's) was gutted and rebuilt in the late 60s after a severe fire. This included interior walls, plumbing, insulation and wiring. Unfortunately, many circuits have few loads, while some are feeding many unrelated loads.

The original panel is quite messy inside. It's tiny and packed with wires; not a neat job at all. My goal is to have some free spaces left over for possible additions after separating the circuits that have unrelated loads.

For example, one 15A single-pole circuit is feeding 4 basement lamp holders, bathroom ceiling and vanity lighting and exhaust fan, the ceiling fan & light of an adjacent room, patio room outlets and lighting, washing machine, and outdoor entry light. I've never had the breaker trip for this circuit, but I can't let it go without getting it in order.

My largest consumer is the electric dryer. No central air conditioning, water & space heating and cooking range are all gas.

Can I replace the 30A 4 space sub-panel with a 200A main lug convertible panel (Looking at Square-D QO13040L200GC), upgrading the breaker and feeder to 60A and #6 copper? I'd be able to put the 4 existing sub-panel circuits there, as well as the few circuits I want to separate.

A complete service upgrade and new panel is not in the cards right now, but I'm thinking down the road, I can have the Square-D panel converted to Main Breaker, and have the service upgraded to 200A, feeding the Square-D, and using the existing GE panel as a junction box to extend the original circuits to the Square-D panel.

Any ideas or insight?