While some might feel the number one reason for growing plants from seed is because it's less expensive, I say it's because it's more exotic. Can you find rich and buttery Nasturtium like 'Cup of Sun' at your garden center? Would it be worth it if you did? It's so easy to grow from seed it just doesn't make sense to buy it in plant form.
As for Salvia 'Coral Nymph', it is partly a matter of expense, because it takes a lot of plants to really make a statement. I've grown this particular cultivar of Salvia coccinea several times, and actually feel cooler by looking at it. Not quite coral, but not really pink, its color goes better with true red or even purple than anything in the pink range unless it's magenta. I'm mixing mine with Zinnias, another easy seed plant.
I'm trying a couple of new Zinnia varieties this year. So far "Cha Cha Cha" is the only one that's begun to bloom. This variety is from Renee's Garden Seeds. A summer without Thunbergia alata isn't necessarily cheerless, but it's certainly questionable. I started years ago with a hanging basket into which I'd sow half a dozen Black-eyed Susan vine seeds. It grew prolifically in an eastern exposure. Those were the species--pale yellow but pretty nonetheless. But now there are hybrids available that leave the old Susan by the side of the road. When Thunbergia 'Blushing Susie' came along, I had to see if she was as colorful as she looked in her beauty shot on the Thompson & Morgan website. I'll let you be the judge. I especially like the picotee edge.
It's not too late to try a couple Zinnia seeds, and maybe even some Nasturtium or Thunbergia. Growing unique plants from seed is certainly something in the You Can Grow That realm.