Few events have unlimited volunteer or staffing resources.
A clear understanding and plan for how you will be using your event site can help focus your team's efforts on the Look and Feel pieces that will actually be seen and used by the public.
Creating an elaborate Homepage with custom colors, logos and images makes the most sense for events directing their supporters to multiple public features at the same time (eg in promo materials, "click here to buy your tickets; donate an item or service and to check-out the fabulous items already donated. . .)
If your organization has another website that your supporters already regularly visit, you may get more traffic to your event site by providing direct links there to "Buy Auction Tickets" "Donate an Item to Our Auction" etc rather than encouraging them to find and bookmark the event website.
If your promotional materials are targeted to specific supporters or activities (eg. donors vs attendees), it's usually more effective to provide direct links to the appropriate feature (Buy Tickets, Donate an Item, Catalog etc.) rather than to the homepage. The more site navigation required, the more likely marginally-motivated users will abandon the effort at the first hurdle. . .
Websites are tools - so when in doubt - choose function over form. Select fonts that are easily readable. If you opt to add custom colors to your themes - be sure to review all pages of the website to ensure there is enough contrast between font and background colors to be legible.
If Volunteer/Staffing resources are especially limited, be aware that the ROI for website "decoration" is minimal to non-existent for non-profit fundraising events attended by a known community of supporters. From a fundraising perspective, you'll make more money by investing those wo(man) hours in obtaining sponsors and in-kind donors, procurement and increasing attendance.