No doubt about not having a low beam. If I didn't already have the light I used, I would've opted for a single unit with a low/high. Would probably be a good idea to add a high beam indicator too.
It certainly crossed my mind about avoiding having to build a sturdy battery box. Little things like that do eat up some time. Another reason for the capacitor is I'm tired of trying to keep all the vehicle batteries around here, charged up. Several of the vehicles sit for long periods between use. Capacitor don't care.
The super capacitors (in a bank) wouldn't be any larger than the giant one I used, but would be about the price of a decent AGM battery.
What's gathering steam right now is a hybrid battery of sorts, where a smaller lithium battery is used in conjunction with super capacitors. Light weight and compact, but still powerful enough to start engines. The battery quickly charges the capacitors and they do most of the high demand work, then once the engine is running what little energy it took from the battery, is quickly replenished. More circuitry though, to keep everything balanced and charged.
For something like a Big Red, that may mean a lithium battery with 1/4 the CCA (tiny), but with actually more cranking power from the capacitors. A downside is not being able to crank it very long before having to stop and let the capacitors recharge. A problem it solves for lithium batteries is their sluggish cold performance.
It's something I'm going to try on my vehicles.