Never have gone by myself, distance and cost being the issue but have thought about it long and hard. The most people I have been to GenCon was 9 but mostly it has been me and one other gamer.
The pros:
The cons:
- Someone to hang with - sometimes a wing man is a good thing
- Reduction in cost
- Backup driver & someone to talk to for 10 hours on the road (for me)
- Someone to hang with - deciding what to do, you can be talk out of something you want to do
- Increase of cost
- Long drive by-yourself
How can it be a reduction in cost AND an increase of cost?
The pros of more that one person / The cons of just one person:

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.