Yeah, double post, I know...but from talking with some folk, I came up with an alternative and wanted to see if anyone had feedback on it. This is still rough, and I haven't nailed down some of the numbers yet...but let me know what you think.
When a spellcaster connects to a spelljamming helm, they decide how many levels of spell slots they wish to dedicate to the helm, ranging from zero to nine. Whatever they decide, the spelljamming helm consumes one spell slot of that level or lower, and produces an SR in-line with the amount of power it was given. If the helm attempts to consume a spell slot level for which you have no spells remaining, that level does not count towards the power fed to the helm. A spelljamming helm can operate at minimum performance by simply feeding off the ambient energy a spellcaster produces, effectively operating at 'cantrip' level.
Example: A wizard decides he wants to operate a spelljamming helm at third level. When he connects to the helm, it consumes one first level, second level, and third level spell slot (technically, it also consumes a cantrip, but those are infinite). The helm is now powered at third level.
Example2: A wizard who has done some fighting today wants to operate a spelljamming helm. He decides to use slots up to fifth level to power it, however he has already used all of his second level spells today. The spelljamming helm consumes one first, third, fourth, and fifth level spell slot, but there is no second level spell slot for it to consume. The helm is now powered, but since it was missing one of levels of spell slot it needed, it is only powered to level 4.
While a spellcaster is connected to a spelljamming helm, they are incapable of casting any spells. As an action, the pilot of a spelljamming helm can break their connection with the helm, shutting it down, and freeing them up to use whatever spells they have remaining (you can physically walk away from the helm without disconnecting, but as long as you are connected you cannot cast spells. Naturally, you can't control the ship if you aren't in the helm). However, if you disconnect from the helm, it powers down and must be fed new spell slots to power it up again, and powering up takes some time (TBD).
In order to change the performance level of a spelljamming helm, you must disconnect and restart it.
I think this strikes a much nicer balance...thoughts?