I think if your travel is "limited" to city hopping, yeah, a lot of them look and feel similar. Certainly, there are unique things about each individual city that make them different, but it's tough to say whether Tokyo is better than Singapore is better than Dubai is better than NYC is better than Sydney is better than Brussels. But most of them have their own unique flavor, food, music, etc., so from that stand point, no I don't think it's "vanilla."
My most recent adventure overseas with my wife was Adelaide (AU) - Sydney (AU) - Fiji. All three very different places; all three awesome in their own ways. Having done a lot of travel to a lot of cities including all of those listed above and others (Doha, Perth, Madrid, Rome), what makes them unique is the history and the culture. In the middle east - Doha, Dubai, Abu Dhabi, Manama - those cities are all very much the same to me excepting scale, but totally different than Tokyo or Singapore or other Asian cities from totally different cultures.
I think if you limit your travel over a particular period to a particular continent or overall cultural set (i.e. all Middle East, or all European) the lines can really start to blur and maybe seem "vanilla", but I feel fortunate to at least have been exposed to so many other cultures and cities to see that there are massive differences between them so that I hope to never get bored with travel.
Two top "next adventures" for me are Florence, IT and a Rhine river cruise.