Newbie Needs help with front shocks on two bikes

Ok so I am pretty new to biking so I apologize for my ignorance. I have a 2005 giant reign 3 with a Manitou Splice Elite, 130mm travel front shock . When I bought they bike my LBS upgraded the springs to heavy duty ones since I am 240 pounds. After not much riding over the years I noticed the front shock was leaking so they replaced the seals. I also ride a trek 3900 which has a spinner grind on it that seems like it going to break at any moment. Here’s is my question. Shoud/Could I upgrade my reign with a better front shock and than put the Manitou splice on my trek 3900 (will it fit?), or should I put something like a Rock Shox Dart 3 Fork ($139) on the Trek instead? I found the Marzocchi 55 R '08 for $239 and Rockshox Recon 351 Coil U Turn FRK 08 Oe $219 and would consider putting these on the Giant Reign3. Would these be an upgrade over the Manitou Splice with the heavy duty spring kit? I am on a budget and would like something as economic as possible thanks for your help and suggestions! :madman: