R-value benefits?

We have a 1920s bungalow with an enclosed front porch. Actually from what I've learned from some of the neighbors who knew the original owner, it was never actually a porch because it served as his barber shop. Anyhow, we would like to use the room comfortably year round but it is quite chilly. The outside walls have windows all around. I would like to add insulation to the crawl spaces underneath to hopefully make it a bit warmer. The insulation there now is starting to come down. Do I need to take the old insulation out before adding new or can I apply over the old? If I apply over the old, would I apply the paper side up so that I can still see the fiberglass? We use the crawl spaces to store lawn/garden equip and would still like to do so which is why I haven't really considered blown in insulation. I would like the rigid foam insulation but the r-value isn't as high as I would like. Suggestions? Thanks for your help. These forums are fantastic. So many questions, so little knowledge.

hi, recently purchased an old house in Hawaii that has an attic and a slanted roof. would you recommend installing fiberglass installation under the roof or on the floor of the attic? We have two solar attic fans in the roof and do not plan on using the attic for anything. the attic is about 4 feet high in the very center, and goes out about 15-20 feet on each side. we've gotten advice going both ways. Mahalo! kfunasaki