Decades ago when I went to Uni I left my nice smart bike at home in favour of an old scruffy thing I had. I made sure it all worked extremely well and even swapped some stuff over. The rationale? Simple. I didn't want to lose my pride and joy but I wanted a bike that rode well. My ride for my uni years was purposely scruffy yet great to ride. I could leave it anywhere and it was safe (I did lock it). Other new bikes would regularly get stolen, even cheap ones from the supermarket with cheap to useless gears and brakes. They were shiny and not scratched, they could be sold. Mine was dirty and scratched and so to sell it would take work.
I few years after uni while working abroad someone doing some repairs to my dad's house saw my favourite bike and after saying how much he liked it my dad gave it to him.
I still ride the old one I rode in Uni. It is only a 19.5" frame and I am a bit over 6 feet tall. The bars are low, the seat is high. The gears still work well. The wheels are still the ones I made as a teen. It has a very long stem to make the reach work on such a small frame. It isn't really a looker but hey, when I'm riding it I can't see that much of it.
To me what matters is that it is all in great working order - smooth and comfy to ride. Reliable. Durable. Do I care about looks? Only after all other criteria have been fulfilled, so not really. It even has odd tyres on it at the moment. One is all black, the other has a green stripe round the tyre wall. They are what were available at the different times I needed a tyre. It doesn't change how the bike rides and may help make it less of a target to thieves. Riding it I am clearly not a poser and racing lads don't feel the need to challenge me - it all works in my favour.
In the auto world it would be called a sleeper - a car that looks humdrum but goes like a stabbed rat when needed. Well, the bike functions like that. The engine (me) isn't up to so much these days - age!
Always go for function over form unless you only want to hang it on your living room wall.