I took over three months off, roughly March through May, from ad spends to get sign-ups to the free weekly email at Rhythm Changes. In that time, the free weekly list size's growth was predictably flat. But I'm pleasantly surprised that so far, my new batch of ads has roughly the same great performance I enjoyed through the fall.
The constraint on my ad spend is income. If I billed more hours, charged more, or got big royalties and/or one-time fees, a healthy percentage of my new profits would go into this spend at Rhythm Changes. I'm interested over the summer to make a new set of ads (even if it's not a new adset: I'm terrified of both messing with a good thing and the alternative of trying to catch up to the existing adset's strength) that speaks squarely about the free weekly, as opposed to the gig list webpage. I'll have to make a new landing page for the free weekly itself and see how that goes.