Definitely worth it - as long as you're in it for the long game afterwards assuming you're a gamer you have a solid 6 GPUs to play with or do double SLI combos, sell or donate to family. The computer knowledge and setup you gain from getting into it is worth more than the money IMO.

As long as you under-clock the TDP% power on your GPUs the electricity cost is well worth the profit you make per day. GPU prices rising has more to do with the memory shortage, but some retailers really do overcharge.

Some of the mineable coins - if you're not mining you'll really regret not getting into it. Might want to provide more details about 10 CPUs tho - are they mining Cryptonight or alt coins with GPUs? From all the info I've read and researched about overclocking CPUs that is def not profitable electricity/hash wise. Once you provide more details about your friends 10 rigs/comps or cpus a more detailed answer can be given.

ROI is def a few months to a year atm, but at the minimum with good buys I'd say its 1 year.