yeah ultrabeat is a sampler as well as sound generator.
everything has a different sound. no, ultrabeat can't sound exactly the same as your mpc, but if you put the same samples in, i dont even know if anyone could tell period. bottom line is if you have good drum sounds to use, yes, ultrabeat can make good drums...its not like its gonna destroy your sounds, you know?
organ is very good, but dont pay 1,000 for an organ alone...b4 by NI will do that for far less. keyboard sounds, you mean piano sounds? it has yamaha grands and all the standards but i still find myself going to reason pianos or ivory for better sounds.
logic is sick, but the biggest thing i tell people about the program is don't get it if you think it is like anything else out there. it is not like Fl or cubase where you're getting deep within a few weeks or something...the manual is 1500 pages, and after that most people still read supplementary books. this program takes a very, very large amount of effort to learn and learn well, to the poitn where you're actually getting the advantages it gives you over sonar or cubase.
by the way rumor has it logic 8 is coming soon, this version has been out for a real long time so i would personally say its a bad time to buy, but then again 8 may not come til august or later, nobody really knows, so its your call.