Yes, it's worth it. You can always upgrade later:
http://www.amazon.com/Xbox-360-60GB-LIVE-Starter-Pack/dp/B001HHWFEY/ref=sr_1_1?ie=UTF8&qid=1230224419&sr=8-1
Given the link above, I think it's foolish to buy the pro unless you are sure you need a HDD. The arcade is an incredible value and it's what I recommend to all my friends.