is it worth the money to upgrade a st 4500 to spark ignition ?

There are several places that sell ignitions that could be used on the 4500

This is the most popular guy for converting these engines

http://www.lambertsrc.com/

Air Power Tech used to be Air Hobbies. Do some research about Air Hobbies.

http://www.rcuniverse.com/forum/m_98..._1/key_/tm.htm

not using them , wow , what a lousy company