On my first property we were planning a cosmetic flip based on the inspection report with a mediocre inspector and unfortunately once we got into it I spent close to $60,000 rewiring and making many mechanical and physical upgrades.

I upgraded from Beyond Pricing to Revmax and have a dedicated Rev manager that looks at my properties daily. 

If you've made upgrades and you put 10% down, surely you can get in to conventional and drop your PMI- that is going to save you even more on top of a lower rate. 

However, if you can manage to find the very few who either don't want to be an investment owner or would prefer to upgrade their capital into something more profitable for their stage of life, launch on it.

You could consider a cash-out refinance or a HELOC to access funds without losing your low 3.3% mortgage rate, allowing you to make improvements like landscaping, roofing, or kitchen upgrades to increase rental value.Selling and using a 1031 exchange to reinvest in lower-cost areas like the Midwest could also be a smart move, deferring capital gains taxes and diversifying your investments.

There are some good options for cabin style properties if you have to time and funds to invest in upgrading a unit to the current standards. 

If I live in a $600k SFH and have around 50% equity but want to "upgrade" to a $900k SFH, what would be the best option?

As a side note, in many cases, putting in individual electric meters will involve not only the meters and wiring, but upgraded fuse boxes and possibly upgrading service to the property itself.

Looking to upgrade the ones in my rental.Would truly appreciate any recos, thank you!

I upgraded to the next level because I knew if it helped me get my first deal, or an extra deal.. or made any of it faster or easier... the price paid would truly be nothing in relation to the reward gained.