your power supply is fine. you could have a 650w, 750w or a 1000w like i do and you will still be using the same amount of power from those components. how large the psu is does not affect the draw of the components.
i have an i7-920 cpu, asus rampage iii motherboard (top end) 6gb ram (3x2gb), gtx470 gpu, 512gb ssd, 2tb hdd, corsair hx 1000w psu and you might think that due to my large psu (i got an awesome deal on it) runs really high on the power bill however at idle or doing basic tasks like web browsing it only uses about 162w (power calc says 584w at 100%tdp).
what this means is that at 100% system load (which outside of benchmarks is just about as rare as hens teeth) the system could use 584w. your actual usage will depend on what tasks you are doing. even when i was playing crysis on maximum i only saw a draw of about 420w which will give you a good idea how your own system scales.
my ccfl backlit (older lcd.. not the new led backlit) television uses more than this (175w!)
just because i have a 1000w psu doesnt mean i am using 1kwh on my power bill. most of the time i am only using about .16 for the tower or .33 if counting the tv in the same figure.
now with that said and explained.. what COULD save you money is having a platinum or gold rated psu over a silver or bronze rated one. the difference is how efficient they are at converting AC to DC for your computer. the lower efficiency ones (bronze for example) waste more electricity than a high efficiency model (gold for example). is it worth upgrading? not unless you run the pc 24/7/365 and are constantly running on 90%+ load. unless you are constantly pumping lots of voltage through it all the time... what you save on the power bill is going to be less than what you would pay to upgrade your psu. also you didnt list your model psu. not sure what yours is rated at.
the psu isnt likely an object you need to upgrade at this time. and since you stated a limited budget.... it would make more sense to push money elsewhere into your build.
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as far as upgrading or o/c your psu is concerned....
overclocking is going to use more wattage and require better cooling (more noise).
my i7-920 may be starting to feel its age however its still a decent chip and overclocking would yield some additional performance at very little additional cost.
while i dont have numbers for haswell (which is a little bit faster than ivy bridge) a stock i7-3770k (again... ivy bridge) runs with about 45-60% more performance than a stock i7-920 (yes i know yours is a 930). if you overclock the 920 to the max (say take it up to 3.5ghz from the stock 2.66) the performance difference between the oc 920 and a stock 3770k is much less. lets say between 10-20%.
read this thread for some numbers and user comments
http://forums.anandtech.com/showthread.php?t=2253195
looks like you're running an x58 chipset (just like i am) so overclocking shouldnt be a problem. all you would need is to keep some good case airflow and buy a good cpu cooler (not sure if a h50 is going to be sufficient or not... you could try it)
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as for the case upgrade? if you plan on overclocking you want an open airflow case. you dont want a case with a flat front, you dont want one with limited fan slots. you also want the largest case that you are comfortable with.
open airflow cases = much better cooling = lower temps when oc
more fans = more airflow at lower rpm = lower noise (just airflow noise)
large case = more ambient air = overall lower tempeartures
personally the best options are cases with options for 120 or 140mm fans (at least 2 front, 2 top, 1 rear and i'd suggst 1-2 bottoms. sides are great and optional. if you throw some good high quality high airflow fans into a case (and dial down the rpm to save on noise with a fan controller) you can maintain both good airflow (cooling potential) and lower noise (than running fans at 100% speeds).
buying a good large cpu cooler would also mean that the fan attached to it (or in the case of "large" its typically at least 2 fans) at lower rpms hence lower noise.
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hope that provides some insight and ideas.
get back with your thoughts.
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