To me, the overall setup isn't worth dumping $500 - $800 into just rewiring it. With some time and learning, you should be able to get the wiring sorted / cleaned up yourself. Start with the main power wire, make sure it isn't rubbing anything, has a grommet where needed, fused near the battery, and fix the frayed ends at the amp and or get reducers if required. Then move onto just the speaker wires, do one door at a time, one step at a time. I'd personally swap out that oversized speaker wire with some decent 16 gauge to make wiring it up easier, and would be zero difference in performance in that setup, though this isn't critical and the current wiring can work just fine. If you have the money, or don't want to mess with it, then by all means take it to the shop, but the reality is, shop prices are expensive.