I moved from a 70 gallon into a 105 reef flat, changed the lights (halide pendants) added a rubbermaid sump, upgraded the chiller, slowly upgraded the calcium reactor, added a 40 gallon fish/fuge, upgraded the protein skimmer a few times.
My system was super stable and growing coral weeds until the calcium reactor failed. I upgraded that two or three times with different plastic tubes, replaced the 20 year old pH meter, rebuild the regulator after 2 or 3 failures and recently tossed those for a Carbondoser.
I skipped a lot of details to say this; over the years I've changed out a lot of the parts of the system trying to improve what I have after initially not having the best equipment for the job. I thought I could get by ok with less expensive gear but have routinely upgraded stuff as the tank performance and corals were suffering for a beter ecosystem. If you upgrade, plan to get all the best right up front or else maybe don't bother.
I spent a lot of money by not getting the best equipment up front. I've saved a little on some things but for the big ticket items upgrading is good. Having extra space has obvious rewards and extra requirements for dealing with more water and rock space. Two different aspects of the topic that I wanted to point out.
Too much coffee and pain meds perhaps? I hope this is helpful.
K