"Is it worth spending $20 on one of those "raffle" lottery games?"
With any game of chance the perception will change when the results are known. It's pretty obvious that somebody winning $1000 - $1Million in the last $20 raffle will say it was worth it and some of those people winning nothing will say it was not worth it.
The reason I said "some" is because even though they won nothing, other players might believe it was still a good bet and make it again. Since Michigan has been selling out their raffle tickets quickly, it looks like those players believe it's worth it.
"I mean should I throw down $20 on one ticket or would it be wiser for me financially to just use the $20 to play other games and/or buy scratch off tickets?"
This is mostly personal preference but if you want to compare apples to apples, see which other games offer similar prizes with similar odds betting the same $20. I know some scratch-off players that even don't care if the lottery offers other games; they continue to scratch until they are out of money. With raffles you usually have to wait at least 5 weeks before the drawing so if that $20 represents your entire lottery budget for that period of time, you won't be playing anything else.
"It's hard for me to justifiy spending $20 on just one ticket. Any advice out there will be greatly appreciated."
If you only have $20 and are looking for action and quick results, I wouldn't suggest getting one raffle ticket.