I don't think many signature campaign managers care about merit.
NO, sorry I disagree with you. Some managers care about merits but merit isn't the only thing to be considered as the reasons to pick someone for their campaign's participants. I think you must know about it. See below some examples:
1. Hhampuz
blender.io Signature CampaignYou need to have received a minimum of 5 Merit in the last 120 days in order to join this campaign.
2. CryptopreneurBrainboss
SatoshiDice.io Signature CampaignThe same as Hhampuz above, Brainboss obligates at least 5 merits in the last 120 days.
3. joeperry
Cleobet.io Signature CampaignThe same as Hhampuz & Brainboss above, joeperry also obligates at least 5 merits in the last 120 days.
I also tried to gamble in my current campaign but not too much since I have other priorities that I need to do.
No problem if you just gamble in a small amount. There is no obligation to play there, but it is much better if playing as it is a kind of your support. So, you have done the right way, buddy. Just continue it without burdening yourself for more.