Hi, You can also visit "平溪" if you have time. It is old town as well but the view is different with Jiufen. "放天燈" is a famous activity you must to do there.
you can visit this website http://www.2012skylantern.com/index.html

Jinguashi gold mine is close to Jiufen old street. It is worth to see "黃金博物館".

Jiufen old street has a lot of different things to buy and food to try~紅槽肉圓,芋圓蕃薯圓.... Meanwhile, the view of the old town and the sunrise is very nice there.

Keelung night market: Is a street which sells nice food. I have been there last June. At that time, there were under renovation. So, i didn't have much impression but you must try "泡泡冰" if you plan to go. Keelung is on the way to Jinggushi so if you have time, you can stop here.

Yehliu (geopark) : Basically, it just see the special terrain landscape. There is a bit walk and it has not much trees around. So, it is always very hot there.

No problem!
Taiwan is a very nice place ~
Have a fun there..