Imagine instead you risk your fleet for a higher purpose. A battle could be won by a hair's breadth and with heavy losses, but might still be an definitive success if it secures your control of an important star system or access to a strategic resource.
Indeed, but it isn't the case now, and I don't think more nuanced outcomes would detract to that end either. Right now you have zero incentive to put your finger in the grinder, and I don't see that many things going in that direction either. I mean sure if your colony is besieged by pirates, you may need to take them on despite bad odds, but I'm more talking about all the times you are ambushed in hyper, or caught right after a battle by another superior force, or when you attack that deceptively small fleet only to discover it is filled with level 20 officers. Those instances beg for savesumming rather than buckling up and going through.
My point isn't that there aren't some circomstances where loosing your fleet is preferable to not defending/attacking an objective, rather than in most cases it is not worth it and the punishement is too harsh for those.
Another batch of ideas to smooth those battle outcomes:
An insurance system could help a lot: pay a monthly fee, get some of your losses back. The less losses you suffer over time, the cheaper your insurance get.
Assassination missions that could pay half the money in advance, allowing you to buy a couple expendable ships.
High level mercenaries could be hired for a fraction of the money the player make.
Right now all the money the player make is dependent on their fleet operations (that might change next update though), thus losses cannot be replaced easily. But what about renting unused ships instead of mothballing/selling them? That could create a revenue stream that while quite inferior to what assignements and bounties make, can still help a lot when rebuilding a fleet. (With a tiered tax system to avoid exploits maybe?)
To get back somewhat on the subject: That doesn't seems to be the direction Alex is going for, but paradoxicaly, very easy boarding or salvaging would incentive a lot the "make do with what you find" gameplay he is looking for. As long as the main way to get a ship is to buy it, every players will want the best their money can get. But far cheaper random findings in debris fields could be a worthwhile alternative, especially if new ships would get much more expensive at the same time.
I remember fondly some playthrough back in 0.65 with the multiple boarding attempts in SS+ and expensive ships in the markets. Back then I would mostly rely on whatever I could get after the battles, only investing money in my flagship.