Buck, when I inherited my pond with the house I bought, the previous owner had put zero thought into filtration. There simply was none. There was nothing more than a few small 29 cent goldfish and a ton of plants. The water was absolutely pea green soup. He never fed the fish and just let them subsist with whatever little mosquitoes or whatever they could grab. No partial water changes, no nothing.
For a while, I just kept the pond in that manner (as I had plenty of things to fix inside the house), but after a month I just couldn't take it any more. I felt bad for the fish. LOL! You couldn't even see them unless they came to the very top.
So, I yanked all the plants out, which were mostly heavily overgrown rush and began to consider a filtration plan. I started with a small pond floor filter box, which was the dumbest thing I could have done. The thing clogged up constantly, so I had to yank it out nearly every day to clear. Next, still on a quest for a cheap fix, I bought one of those green tetra bio filters which was a complete waste as I couldn't even get the cover open when I needed to clean out the media.
Finally, I just said to myself, what the hell am I doing? Do I want a REAL pond to enjoy, or am I just trying to help these poor little goldfish get a bit more quality water?
Finally, I got myself the Laguna maxflow and a pressure filter with a UV light. Bingo! Everything started working right. The water cleared within days. I added koi a few months later and then I was totally sucked in. All was fine for a few years like that and then I really wanted to improve the quality of the filtration and pond mechanicals as much as I could without having to rip out the pond. So, I retrofit the whole thing to it's max point. I did everything I could short of pulling the liner out and starting all over again.
I added a retro-fit bottom drain--best thing I ever did. No more vacuuming and mucking for me! I got myself an external pump so that I didn't have to deal with sticking my hands in water to service my pump anymore. And then I left the pressure filter in place, but added the 55 gallon barrel and dolphin AV-50 air pump. This was the magic combination for me that gave me the absolute best water quality. I do all the proper water changes every two weeks and use salt when necessary, etc. My work now is the most minimal it has ever been.
I turn the waste spigot on my barrel open and all the detrius comes out and I add more water. It doesn't get easier than that. If I had to prove the quality of my water, I would have no trouble at all taking a sip.
Koi and goldfish are monster poopers, so I would not keep any of these type of fish if you were to go sans filtration. You'd be better off doing what your wife says. But most importantly, you have a captured body of water....it's not natural. And you need the water to move and get air and be filtered in order not to stagnate band subsequently build up ammonia/etc. that will kill it's inhabitants.
It's up to you, but 1,500+ gallons is an awful lot of water to deal with once it goes sour. I would just set up at least 1 55 gal drum (it's certainly better than none)--and keep your fish stock low (perhaps stick with goldfish--sarassas are inexpensive and look like kohaku koi). Or buy a pressure filter (if you don't want to DIY it). These can be buried up to their necks, so you barely see 'em if you're worried about something unsightly. But I would take a good measurement of your pond and do a water calculation. As I said, your pond looks to be greater than 1500 gals to me.
At the end of the day, you will do what you want since it's your pond. But I will tell you it's much easier to put a filtration plan in place upfront than have to retrofit everything later.
I look forward to see what you do either way.
