So, even if you can win the daily jackpot with wagering 5 BTC (I don't think it's possible), It's like that you are playing a game with 1.7% house edge.
You need to pick your day to try it. Someone won with just 1 BTC wagered one day last week.
Wagering 5BTC in a one go to secure the top spot in the wagering content are high risk bet, I cant imagine risking 5BTC to win .13 BTC

How exactly the prize are being computed on the wagering contest? Or it just go up like a count up timer with specific sats/sec?
The prizes are going up all the time as the timer counts down from what I can see,,, I think it depends on how much is being wagered on the whole site though because sometimes the value jumps a lot.
I can definitely imagine people wagering 5 BTC, and that is normal betting. But to win extra .13 I suppose I see it as an additional bonus.