For your first question, yes it does make a big difference with the heavier weights. My buddy got heavier weights in his Newport 2 and you could feel a big difference in head weight. Regarding your second question, I don't know anyone who has gotten their putter customized in the custom shop but I've seen what can be done in there and if you are going to get it done I don't think you will be disappointed with what you choose.

I just did some weight changes last weekend see the difference in control and feel. Nothing drastic 10 to a 20 gram change. There was definitely a noticeable difference in just adding 20 total grams to the weight of the club, the heavier weight had the ball rolling quickly. I honestly preferred the stock 10 grams, but that was in the heat of the afternoon with things rolling quick. I will test the 15 grams this weekend and see if it's a good middle ground for me. The heavier weight may be the choice in the colder months, but that's a ways away.
As for the custom SC logo's on the weights or even a full color change, that's a personal preference and like you said, what makes it yours.