If everyone gives up mining bitcoin will end up centralized.
If you hold a sizable amount of coin I think it's only wise to invest in network diversity a little bit. You will not get rich though, that's for sure.
I'm just talking to newbies here.
I don't invest in mining cos because I think there is too much people throwing around money cause it's the hot thing now. In general I am amazed at the willingness to take risks without compensation. I don't follow it very closely now, maybe it has gotten better last few months. I'll wait until the dust settles and invest then, mining cos are almost the only companies that you can invest in if you believe in a significantly higher bitcoin price in the future.
(For those that haven't thought about the consequences of having shared denominated in BTC: If you buy shares in bitcoins in a cheese-company and they have income in $/ then their income seen in BTC will halve if the bitcoin price doubles, and the shares will go down. Mining companies have their income in BTC and some expenses in fiat, so they will only benefit from higher btc-price)