Do you think it is worth purchasing the Global pass for non-concecutive days?
Please provide more information about your itinerary. Railpass can be great deal depending on time in Europe, number of countries, number of people traveling together, etc. EXAMPLE: I took my wife and her mother last fall and we got the saver pass, which allowed us to travel for five rail days within a two months period. We were there 10 days and traveled from Rome to Florence, Florence to the Cinque Terre twice (and between towns while there) and the night train to Paris near the end of our trip. Only stipulation, we had to travel together because it is a single ticker for all. Worked perfect for us. If your train travel is limited, you may be better off buying point-to-point tickets, either online or at the train station. Faster trains require reservations that cost more, and you should buy as far in advance as you can, especially for the night train. If you can provide more information, you'll find many responses with great information, which is what happened to me when planning our trip. Good Luck.
PS Check the railpass section on this website for GREAT detailed information.