the challenge of how much to add to a quest is part of the jam.
I won't personally advise how much is too much, but I will be frank here - a judge who decides the creative aspects of your quests is worth the work to build it may judge the accessibility accordingly (mercifully), and another judge who does not see the point of additions may deduct.
Using base assets is "safe", but trust me when I say that there are quests that will use a LOT of assets in a way that will rank just as highly. It's subjective and there will not be a mathematical formula that gaurantees anyone a win.
I want to see quests that you, the participants, want to build - the ones you are excited to make. If you worry about chasing a high score to win and put aside your creativity, your quests may suffer for it!