Learn something everyday..... I have never seen a residential 100A. Service with a fuse box. Yes...Electrician by trade.
Not an electrician and I have seen many of them, my house included.
I just went from a 100a fused panel to a 100a breaker panel.
To the OP, unless you plan on running a lot of power for some reason, you do not need to upgrade to a 200 a set up.
I have a 100 a in my house with a 100 a breaker running my detached garage 100 a panel, yes it meets code here and was with a full permit and inspection.
I have in floor heat in my shop running off of a tanked water heater that is electric in addition to my 220v compressor and welder, etc.
I have never had an issue with running out of power and tripping either my shop panel, in house breaker to the shop panel or the main in my house.
The upgrade to 200a was a significant cost so I just stuck with the 100 a and upgraded my panel to breakers. The only reason I did that was because I was finishing my basement and had no room left in the fused panel for all the basement electrical I wanted. Otherwise I would have kept the fuse panel, as noted they are actually safer as the fuses blow faster and more accurately than a breaker.
I too was stuck on getting 200 a upgrade until I had my electrician friends over to discuss my ideas and they ask why 200 amp? After some discussion I went with what you read above. I really didn't have the need for it. Add up the amps you would need to run multiple items all at once and you will likely still be under 100 amps.