A used SP10 for $1000 is not a good investment. Bitmain S3s are $200 each for 450GHs (plus shipping). And they're much quieter although you will need to get a PSU or two. SP10s sound like a jet engine and are not suitable for mining in a normal residence.
And how long will it be before your landlord starts complaining about your excessive electrical usage? Believe me, they monitor these things closely.
How much electricity costs on average (per day) would a, say 1.4THs miner generate? Im pretty much clueless in that regard. I do think it would go unnoticed however (I live in a student apartment with a couple roommates)
As per sound, yeah, I wouldn't want a jet engine, but noise in itself is ok.
Basically, I want to get into mining, But only if it will actually be worth it. $ wise (not taking into account possible drops in btc price)
Your electricity costs depend on the efficiency of the chips in the miner. The SP10 on standard US 120V power can get you about 1.4TH/s by overriding the default power limits. It will use about 1250W to do so. The SP20 will get you 1.7TH/s and costs $795 USD. You will need to supply a good efficient PSU (I recommend the EVGA 1300 G2) to power it - another $150 - $200 USD or so. It uses 1150W. So, if your electricity costs you $0.10 per kWh, then your power costs would be 1.15 * 24 * 0.10 = $2.76 per day, or $83.95 a month. You might get away unnoticed by your landlord.
As of right now, that 1.7TH/s will expect to mine about 0.02121
BTC per day.
You could also go with the Antminer S4. 2TH/s for $1200 USD. There are a ton of $400 off coupons floating around that expire the end of this month, and it has a PSU included. Uses about 1400W. Same formula as above, power would cost 1.4 * 24 * 0.10 = $3.36 a day or $102.20 a month. Expect to mine 0.02496
BTC a day right now.
As has been mentioned, when difficulty changes, so do your expected earnings.
Even though the S4 uses more electricity, the extra 300GH/s it offers would make up the cost difference and then some - at $375 per BTC, as of right now, you'd make about $280 a month with it, vs $240 a month with the SP20.
So... forget the SP10 and consider the SP20 or the S4.