Hello,
We have 7 years of experience in developing installers using WiX and NSIS. Please refer to my work profile GenesisBuzz on Elance & Freelancer. We have developed more than 40 installers on Elance, Freelancer and offshore projects. We have developed couple of installers which run on the concept of upgrade.
Please let us know if we can demo you some of our installer work and feel free to ask us any questions you may have.
Thanks & Regards,
Vighnesh
GenesisBuzz