The plugs are alright, no signs of burning I can see so far, no overheating (never before) and not sure about any leaks with a quick inspection.
So only the scary sounding stuff up there are what need more inspection to make sure of them. The thought scares me, tho. I rebuilt the engine ~62.5K miles ago.
However, I used Abro Stop Leak powder (that's against my beliefs) this morning and since then the coolant in the reservoir stayed the same. I drove ~100 miles since then under ~40C ambient. I followed the instructions faithfully... which scares me for some reason.
So, fingers crossed, problem solved?!?!?!