Actium

Both functions take Lua code as a string argument. net.dostring_in() can only return a string, but a_do_script() can return tables, too. However, its return value pass-thru is currently somewhat broken.
If all you want is getting a group template, just unzip the .miz file, open the extracted file named "mission" with a text editor and get the group data from there. No need to deal with traversing and converting the table programatically. Just copy & paste.

I absolutely agree that the user files need a user-experience improvement. However, I do not expect any short-term wonders to that end.
A possible workaround is to use a search engine with the site:www.digitalcombatsimulator.com/en/files/ parameter to restrict the search results to DCS user files. Example with Google and "tourist".
P.S: Not addressed at above posters, who I'd expect to be fully aware of that option, but rather to help the less tech savvy DCS users make better use of the user files right now.

Dummy response to mark as solved.

The master server was down for half an hour shortly after midnight UTC. That took down all clients and dedicated servers. I've reported the issue here a month ago:
 

This issue has been fixed in DCS 2.9.14.8222. Unserializable values will now be substituted with null. The following example code
local t = {a = 1, b = 2, d = 4} t["c"] = t return net.lua2json(t) now returns {"a":1,"d":4,"c":null,"b":2}.