A few weeks ago friend and Dirty Dozen designer, Pam Hooten, was amazed that I can stamp so many cards in one sitting. She mentioned if she could stamp like me, she'd never be behind on birthdays! I 'fessed up to my secret. I cheat. I use the same layout and prep a ton of cards with different patterned papers & the same layout. When you use an assembly line type process, you can keep cards on hand and slap on a main image when you need a quick card.
Here's how I do it. I take and stamp the same background (canvas) in the same color (creamy caramel) on different colored cards, all at the same sitting. I may do 12 to 15 of these cards. Then I layer different scraps of patterned paper on that match. Choose your cardstock colors based on what will match your patterned paper.(See above)
Then, later on, or even in the same sitting, I'll add a main image to the card. You can use the same image with different color combos, or mix it up and do all different images. See what a different effect the same image has on each of the 4 cards? And your friends & family will never know it was mass produced, as each card is different, yet the same.