It's all about showing them that you have been paying attention to their taste, what they like and dislike. i think this is true for any gift, not just romantic gifts. For example, I have a friend (who is a bit of a hippy) who practically melted when a guy she was dating left her a pot of dirt on her doorstep with seeds planted in it. I'm not suggesting you leave someone dirt--the point is that this guy knew *her* well enough to know that she was not your average woman and wouldn't want cut roses, even if they were in a huge expensive bouquet--she was the type of person who was more excited by the gesture of seeds growing. His small gesture showed he was paying attention.
I was living abroad once and someone sent my roomate a box of autumn leaves that were all red, orange, and yellow, so that she wouldn't miss out on the fall colors even though she was 10,000 miles away...thoughtful gifts don't have to be expensive...even leaves picked up off of the ground can be romantic if they are presented in the right way.
Overall, I would say that handmade things are very sweet because they show you've spent time on them. There are some women who value money more than time, but hopefully you've found one who would be won over by a hand-made card with a poem inside.