In the days of the Alberg 30 the engine was an auxillary basicly to get you in and out of port. It is afterall a sailboat . 10hp is enough if you plan to sail. By modern standards it is underpowering but way too many sailors now no longer pull up the sail they just use their engines . I know of a couple who sailed the world on their Alberg 30 with no engine but thats taking it to the extream. There is no real underpowering in a "sail" boat. A smaller engine will mean you have to depend on your skills as a sailor and you will not motor as fast. Have a look at Ericson 29's and 32's as an inexpensive liveaboard and a well made boat as well.
Best of luck in your search