Resolution or volume is all about managing. Backburner/Other manager is absolute must. Never wait for render, render everything overnight.
But don't give high-resolution images without high-resolution price ;- ). I am not saying to price different resolution differently like in stock-photography, but high-resolution is form of higher technical quality and should be priced accordingly.
I render everything in 8k for multiple reasons. One dominant is that our clients often do print stuff up, and 8k is both necessary for pretty magazine spreads (Often in A3+ kind of size) as well as billboards. But other, I love to show off all the attention to details that go into imagery. All those detailed models, shaders and textures, it looks better if you can appreciate it up close (or in print). It shows craftmanship, and clients do notice.
Similar to photography. Creatively, beautiful photograph can be shot on cheapest phone. But large prints always benefit from large format systems, it's part of the allure of high-end charm.