I've traveled extensively overseas and I never use a travel agent, but it can also be a comfort. If you are fairly independent and willing to spend the time looking for what you want, comparing reviews, understanding rules ( like you need an international drivers license, are visas necessary, etc)- in my opinion, you don't need a travel agent- particularly in an English-speaking country. For me, the planning is part of the fun, but it is alot of work.
If you do it independently though, I do highly
recommend booking at least one small group
or private guided tour. Most things can be toured independently, but you'll never get the level of insight/ understanding of what you are seeing in a guide book. Meeting the people there and understanding their views is also a huge part of the experience; they can also get you into the great local place you would have totally missed on your own. These tours can be pricey, but after years of doing everything self-guided with lots of guide books, these are now a mandatory part of any of our trips ( in fact I'm booking a private food tour of Parma & Modena this week as part of our Italy trip in May