Gambling is totally worth it. In short: reclaim the coupons that you can, sell the ones you can't reclaim.
How useful the things are that you get depends on your tech level. Higher coupon levels gives better things. There is a whole line of quite good weapons (golden) you can only get through gambling. It's gambling, so you will always get some junk as well.
If you gamble just to make money: I tested the copper and iron coupons, and for these reclaiming them and then selling the stuff gives you more money than just selling the coupons. This is on average, so if you reclaim just five coupons chances are it's lower. It should also be noted that gambling gives you a steady supply of apples.
Gambling is most profitable when the things you get are actually useful to you, since getting them from gambling is way cheaper then buying them. I found gambling the most useful when I need to equip troops for a newly established base.
Gambling can give you things way ahead of your techlevel or rare items you don't have yet but need for research. Here is a short list of things I find useful:
copper
- Maid outfit (research needed for Mansion mission)
- exquisite lingerie (you need a lot for seductress outfit)
- wrench
- old coins (bank bounty tokens)
- electric lasso
- boom fruit
- mine
- zombie juice
- vampire blood
- animal poison
- human space suit
- riot shield
- dart pistol, with basic or advanced ammo (basic ammo is extremly useful underwater)
- precision pistol
- combat shotgun
- crusader slave armor
iron
- all the useful things from copper
- old earth books
- Lokk'Naar scripture
- celatid essence
- Jack bounty tokens
- panzerfaust
- LASS
- knockout grenade
- all kinds of powerful explosives like, satchel charge, high explosive and barrel bombs
- aye phone (motion scanner)
- crazy Hassan flyer
- poison gas cannonballs (so useful for deep one pogroms)
- lynx smg
- painbringer smg
titanium
- boss armor
- doom slave armor
- grav harness
- vibro blade
- vibro sword
- bardiche
- super-self-charger
- demonic essence
- hypno panel
- stasis grenade
- rcf carbine electropulse ammo
- haxxor
- raygun
- omega rifle
- golden pistol
- bunch of heavy weapons like mortar, rocket launchers and grenade launchers
- and much more...