Don't want to beat a dead horse, but compared to the Suica/Narita Express deal, the Keisei line is only 200-300 yen cheaper each way. (You can go all the way to Shinjuku on the N'Ex.) But the Keisei has no space set aside for luggage and takes three times longer than the N'Ex. Mind you, when I go from Tokyo to Narita, it's Keisei limited express from Ueno all the way - no question. But flying into Narita and then heading to Tokyo or Yokohoma, you're doing yourself a disservice by not taking advantage of the Suica/N'Ex deal (which is only open to people with a foreign passport, btw.) Then, if you want to take in the ambiance of the Tokyo-Chiba urban sprawl, hop on the Keisei and enjoy the scenic route on the way back. Incidentally, Shinto Gangu is only open an average of two days/week these days, so check the website before you go there. This week, the shop is open a total of 5 hours.
I totally agree, Sunroute Plaza Shinjuku is the best in that range I've found in the shijuku area. It's clean, friendly staff (but I've never been anywhere in Japan were there weren't friendly staff) and very well positioned (some great Disk Union stores walking distance if you're after records too). I prefer Sunroute to other hotels like the Park Hotel, which may cost a little less but at least as far my experience goes wasn't as tidy.
