any relationship needs some cultural similarity and shared interests, activities, hobbies, etc. otherwise there's nothing to do but fuck, or you just into one of the those couples silently eating breakfast reading the newspaper.
extraverts are good bc they make us introverts try things that we normally pass off as unworthy of our time and unfit for human consumption. we need some enthusiasm (entheos!) to get us going like when it's cold out and you exert yourself and the blood starts to flow and your cheeks turn red. it feels really good to be alive.
infj + intj is good for introverts who do NOT wanna change, for whom expansiveness is entirely an interior category or who are extremely focused and dedicated to a single work-related pursuit, and who as a result value their introversion more than they will ever value being pushed, nudged, stretched, and pried open with a crowbar.
intj IS the ultimate clarifier for infj, but it does not shower the infj with inspiration like some other types. and we want to live, dammit! we want emotional currency flowing thru our veins! (eh, or maybe i'm just young and immature and nostalgic for pasts that don't even exist)
with that said, as a mutually beneficial mature relationship, it is rock solid. sharp edged, but rock solid. it totally depends on where you're at, your focus in life, what you are trying to develop, work on, cultivate, etc. and how committed you are to making it work alongside and in cooperation with your other pursuits. has a very natural partnership feel to me.