This is MAJOR weakness in the Marriott program. There is a huge leap from 15 nights to 50 nights a year, yet the benefits for GOLD are minimal over SILVER! I have been SILVER for a few years and really don't see any reason whatsoever in going for Marriott GOLD. An extra 5% in bonus points--pinch me! "Upgrades" when available--I have heard of very few who actually get an upgraged room--many Marriott hotels have no suites--only one kind of room, just on different floors. Concerige level--yes, but that's about it!
Once I hit my SILVER level, I look around at my choices of hotels other than Marriott.