I haven't been to Little Cayman, but I've dove Grand Cayman a few times. There are several shore dives which are worth doing; however, outside of the Sunset House, the resorts are not really set up for shore diving and on site dive shops won't allow outside tanks. The upside is that when we were last there a couple of years ago, tanks were running 6$ to 8$ US and weights for about $2.
In the George Town area, the Sunset House has a decent shore dive with the statue of Aphrodite and has some reef formation.
A little north in downtown is Eden Rock Dive Shop with the Eden Rock/Devil's Grotto out in front. These adjacent sites have lots of cool swim throughs and usually a few tarpon. They run pretty shallow (under 40') and make for cool night dives.
A few hundred yards north is the wreck of the Cali. This used to be the home of Don Foster's Dive Shop, but I don't know who is in the building now. This site is basically a debris field as the wreck has long ago broken apart. Its pretty shallow (around 30') and due to boat traffic, you have to drag a dive flag with you. There are also some large coral heads on the south side of the wreck where you can often find tarpon.
There is also a good mini wall dive in front of Dive Tech just north of the Turtle Farm north of 7 Mile Beach on West Bay Rd.
Grand Cayman also has cheap and fairly reliable public transportation (white mini van bus service) that could get you to and from most any hotels in the 7 mile beach or George Town areas and any of the dive sites I mentioned for around $2 each way. You can just carry your dive bag on the bus and pick up tanks on site.
With that said, have you considered the Netherland Antilles islands of Bonaire or even Curacao? If you are looking for unlimited shore diving, you can't beat Bonaire and Curacao has similar divng with more top side activities. The shore diving is outstanding and fairly cheap (an example, Bonaire Dive and Adventure offers unlimited tanks and weights for six days for only $105 and Nitrox for the same) Now that Continental is flying Houston to Bonaire and Newark to Curacao, the Netherland Antilles is alot easier to get to and generally cheaper for hotels, diving, and food than the Caymans.