No, never. It’s a <10 min. job to flash and configure a new card if needed (when it’s only used as RoonBridge zone).
Your upsampling numbers look fine – I agree that these should not cause any problems.
As for the Cuboxes: I have three of them around the house (i1, i2 & 4Pro). Even the i1 does not break a sweat when running RoonBridge.
I run Armbian on them. If you decide to dive in, make sure you use the Legacy release (Vanille was pretty half-baked for audio last time I tried). They changed their site a bit, offering only Ubuntu Vanilla on the first page – but I guess you need Debian_jessie_default these days, available from here: https://dl.armbian.com/cubox-i/
I touched on the Cubox installation in the old guide (instructions come after the Raspberry Pi part). You can ignore the bit about .raw files – Armbian uses .img files now that you can write to your card in the same way you’d do with DietPi.