Im unsure what the minimum spec is atm as @abits patch addresses some of the previous hardware issues like ram. i asked a similar question in mining chat. here a reply from @bitcoiner "I don't think the hashrate and in turn the number of pows found and blocks produced relate to the hardware specs anymore as it used to, because with abit's mining shortcut, you aren't actually doing work and just keep submitting"

I believe with @abit's code you don't need as much ram as its using virtual ram so i think people will be able to mine with a lower spec than before. all i can say is give it a try. what spec machine do you have?

with regard to how much steem you can expect, unfortunately its currently not a lot atm, maybe 1 or 2 steem per day. but as with all crypto-currencies things change over time. bitcoin wasn't worth much originally and now look at it. so those few steem might be worth a lot in the future. also mining algo's change so there will be more efficient future mining as time goes on. As its not really costing me to mine atm as i have my pc on all the time anyway, i might as well keep mining so i have knowledge and experience for when things do change again.
Also i would like to be a witness so this is experience and not wasted time even though it doesn't return me much revenue.
Another thing, you can also use mining to create new accounts