Honestly, most kitchens do not need more than 4 knives. I own and use more, but I cook a lot, and have very good knife skills. I can do almost anything I need with a single large knife (ideally a santoku, but a chef's knife or chinese cleaver would do ok as well). One serrated knife for bread.

The most important thing is that whatever knife you use is good enough to hold an edge, and kept sharp. Have your knives professionally sharpened at least once a year (or learn how to do it yourself) and use a steel to hone them once a week or before/after any hard use (1/2 hr+ of prep chopping). It's also worth some time learning proper knife technique.

All that is much more important than having more than two knives, as long as your two knives are good choices. When I vacation in cottages with a kitchen, or when I visit relatives that I know do not maintain sharp knives -- if I will be cooking, I make it a point to pack my own knives (I bought a chef's knife caddy from a local culinary school for this purpose). And I am a massively nazi-ish light packer, typically packing for a week+ trip in a single carry-on bag (including my knives). That's how important this is to me. That said, I love cooking, and tend to do a lot even on vacation.

I think this principle generalizes. Tools are a nice force multiplier. For anything that you love to do, or need do frequently, having good tools that will last a long time is generally a hugely efficient upgrade in your QOL.

It can, of course, be taken too far. Upgrading everyday use tools to cheapest professional grade is a very good use of money. Upgrading to the best possible, or upgrading things you rarely use is generally not.