Database versus Files for Solo Developer

I suggest you to add Spatialite to your list. It has the benefits of being file based (as a shapefile, or an .mdb database) and supports most of the usual spatial operators and tpyes, that you can find in PostGIS too. Spatialite is based on Sqlite, so you will manage a single file, that you can easily move and share.

I'd say the biggest Pro on a PostGIS database is, that you can work with the whole function set PostGIS gives you.

All the Cons in your list, are all very easy fixable. You can run Postgis on ONE server and use your laptop and desktop as a client. The backup question as well, you can generate dump files or what-so-ever to have a good and valueable backup! ;)

Another big plus for PostGIS is that with spatial databases you can keep one copy of the spatial data and create views that link to your non-spatial data via a unique id.

Then you can create subsets of your full data by creating views that select from it - so you can do single-state tables as views of a full country table. SOmething like:

create view txcounties as select * from counties where state = 'TX'

Also nobody seems to have mentioned the speed of spatial operations for PostGIS. Suppose you want to see what the nearest waterfall was to your bike trails, given a table of lines of trails and a table of points of interest including waterfalls. That's the kind of query that PostGIS can do really quickly since it keeps spatial indexes on the spatial tables. You can probably do it with the native tools in Qgis but it might be quite a bit slower.

Obviously for a fun little application like yours these things are probably not a good reason to get into the complexity of a spatial database, but it might explain why these 'enterprisey' features are essential for bigger projects.