version control is really useful if your developing with other developers where you can branch out and write code without affecting each other until you do a merge. (its even better with distributed version control when developers are at remote locations with poor data connections)
In your case, if your working on your own you dont really need version control unless you'd like to see your past commits.
This is wrong. Version control offers you advantages when you're working alone. The main obvious one is a history so when you mess something up, it's an issue bisecting or rolling back, something you're not getting working direct with files without forward thinking and making sure you never forget your procedure. All code should be managed, always. Then backup the repo and not tons of code instances on ton of different servers.
To answer your question, no you dont normally merge versions of the same file from the same branch but you would be able to look at the history of the file and reimplement the fix for the file and commit that.
Actually you can do this type of stuff in git and don't need to sit reimplementing code. You should read up a bit on git fully, it does a ton of stuff you'd never actually know about until you read the manual.
If there is one person, you can do this equally well with Git or SVN.
I disagree. Sure, you can avoid the majority of SVNs issues by being the only person working on a set of files and making sure you work on things / commit things in order. Then again, you're asked to do a major project to your code base, you do the right thing and make a branch (you can't not commit to the trunk while you work on this project, obviously). While working on this you then get a different project prioritized, so now you have two branches. All the while people have been bugging you about small changes to the trunk. You're context switching and now have 3 different code bases, playing the system just like it has multiple users and you're going to have to deal with SVN merge which is where a lot of the whining about.
Theres also the fact SVN is typically slower than git and it's a pita.
Don't get me wrong, using SVN is a lot better than using nothing but anything learning new and any new projects should probably use git. You can argue that other DVCS are superior to git, but git probably is and will continue to be the most popular DVCS for quite some time.