OK I have a 2003 350z, The passenger side valve cover gasket is leaking up front and the oil is getting on my exhaust and making a horrible smell. So the nissan place said it would be like $500-$600 to replace the gasket. I was wondering how hard of a job it was to do this? I know i can do it but dont really have alot of free time right now? how long does it usually take? Also while replacing my valve covers i would like to do some upgrading where it can be done, such as maybe a intake spacer or kinetix intake, bigger injectors, better spark plug, etc. What is also the best bang for the buck to do while I have everything apart?

Thanks
Billy