When I first became curious about expeditions there was little constructive info on this topic. All the posts I found were from people who had tried it in 2014 or so and had already made their minds about not playing PvP. So I thought as somebody who has played it fairly recently maybe I give an account of how it worked out for me.
I started playing colonies when I was on lvl 36 and during the Holloween event 2016. At the time I did not have any other viable options to gain titanium to slay Golems and that was my last resort and it actually solved my problem. After that I stopped playing adventures because they had become boring and again I needed titanium to train crossbowmen to do the more interesting ones.
During those two month I saw the following things happen:
1) First of all, let me tell you that there has been a couple of improvement since 2014 for expeditions. Training units is generally cheaper and faster now, and the rewards from the conquest of colonies are somewhat higher. The points that follow are by considering these improvements.
2) Doing colonies and adventures at the same time is a terrible idea. With the cap on the number of troops that you can fit on your island, doing both means you are going to be incompetent at both.
3) Colonies do not give you enough XP. In the two months that I played PvP, players in my guild who were on a lower level and only did adventures had so much progress that now I stand a staggering 7 levels below them (I am on lvl 43 BTW). Getting on higher levels in general has an exponential effect on your economic growth, i.e. new explorer capabilities, new buildings, etc, while PvP levels do not unlock anything.
4) When doing some adventures, there is also the possibility of finding nice buildings and other stuff in your loot which again can boost your performance, while for colonies it is always an alternating set of boring resources. But wait! There is always the expedition water castle for you, so I would say that kind of evens it out.
5) Conquering a colony is more involving than doing adventures. First because there is a lot of hit-and-miss involved: the type of resources you get by searching could all turn out to be hardwood and marble, you might have a nice colony which you can lose at any point in time, or you might arrive at an island which is ridiculously impenetrable. Also, iron is an essential resource for training expedition units, and its production cycle is harder to maintain. Indeed I have found out that mining iron and trading it is a much more lucrative enterprise than doingn expeditions.
6) The development team has given up on expeditions, so unlike the non-PvP feature which are updated and extended regularly, rest assured that the future holds nothing exciting for you there!
That being said, I still play expeditions when I am really bored with adventures, because my opinion is that in the end this is only a game. When I was playing games on my PC I would not stop playing because it had one annoying feature or would occasionally crash or something and an online game is no different.