Any time spent in ther air is good. The more time you spend "in the system" (flight following, IFR flight plans, etc...) the more knowledge you will have, regardless of what you are flying or why you are flying it.
CFI'ing isn't all S-turns. I spend most of my CFI time with instrument students, or multi-students (many times at the same time). If teaching a multi-engine student how to manage an engine failure while flying a VOR-A approach without radar vectors, with the weather down to minimums doesn't benefit you, I don't know what would. Just because you aren't in a CRJ with another pilot helpng you doesn't make the experience any less valuable.