First, to answer you questions, you have to either have 1.50 or a custom firmware to play NES emulators.
The point to downgrading is to show sony no one wants just theres and stop being idiots and not letting us play the games we want.lol. just kidding. the real reason is to,like you said, play homebrew games and do homebrew applications.
1.50 is ok but me and everyone else on this site will probably tell you to upgrade to a CFW. A CFW instead of 1.50 lets you still play homebrew games but also gives you what sony is offering with their FW and extra. Such as the biggest examples recovery mode in case of semi brick, and being able to control the speed your psp runs. This can greatly influence battery life and speed of games.
If you just downgrade to 1.50 then it will have a "drawback" which is not being able to play psp games that require a certain version. BUT if you upgrade to a CFW then you will be able to play those games again.
If you need any more help pm me.
The point to downgrading is to show sony no one wants just theres and stop being idiots and not letting us play the games we want.lol. just kidding. the real reason is to,like you said, play homebrew games and do homebrew applications.
1.50 is ok but me and everyone else on this site will probably tell you to upgrade to a CFW. A CFW instead of 1.50 lets you still play homebrew games but also gives you what sony is offering with their FW and extra. Such as the biggest examples recovery mode in case of semi brick, and being able to control the speed your psp runs. This can greatly influence battery life and speed of games.
If you just downgrade to 1.50 then it will have a "drawback" which is not being able to play psp games that require a certain version. BUT if you upgrade to a CFW then you will be able to play those games again.
If you need any more help pm me.

