To Portugal: travel agent or no travel agent

I'm not sure what a travel agent could you for you that you can't do yourselves.
Book your trip through the airline you desire.
Book your travel (Lisbon to Porto or Porto to Lisbon) (I assume train).
Book your stay as it fits your budget.
The forum has much information on what to see/do and good places to stay.

We spent 5 nights in Lisbon and felt it was about 1 night too long.
Has fun.

Thanks. We have now booked our flights on United. Our concern has been if anything goes wrong (hotel, flight, whatever) as it did with one trip on our own to Cancun. If a travel agent is making things happen, would (not) they be able to set things aright faster and easier than we could on our own? Does this make sense?

There are some very high dollar travel consultants that maybe you can rely on, but I would not count on a typical travel agent for much of anything.
You can get travel insurance, but really you are at the airlines mercy when anything goes awry no matter what--but it's a safe country with fairly easy travel logistics, so I would not sweat it.

I was wondering if you could be a bit more specific as to what problems you want to avoid.
This might help with more specific answers.
As for economy or economy-plus, look in the airline website to see if "plus" implies more leg room.

If you're talking about United, Economy Plus provides more leg room than Economy. As one who is 6'3" and with a wife as my traveling partner who is 5'10", I'll do almost anything to ensure I have leg room on a flight over two hours. Flying from the US to Portgual is a much longer flight than that, so I would pay the difference. And if I had the points to upgrade to Economy Premium (United's latest addition to compete with other long haulers) or to business, I wouldn't hesitate. Candidly, depending on the fare difference, I'd even pay for business class just to have the comfort on an international flight.

Last year we flew United's Economy Premium for the first time from the West Coast to Heathrow. In general, passengers in that class are treated at the airport as if they're flying business in terms of checking in, TSA, and boarding -- but you can't use the United Lounge for free. On the plane, you supposedly get the business class meal and drink service -- though one flight attendant erroneously told my wife we needed to pay for our drinks. Most important to me, though, is the seat pitch (leg room). It is better than Economy or Economy Plus, and the seats are wider, too. So it's more comfortable for a ten-plus hour flight. I would fly United's Economy Premium again -- and wouldn't hesitate booking similar seats on other airlines.

One last thing... I don't know of any travel agent anymore who has as much or more juice than a passenger who booked directly with the airline or the hotel or the tour operator who has a problem and is standing in front of that vendor to discuss options. Language can always be an issue, but problem resolution is best achieved with polite persistence and a willingness to be flexible. I'm fortunate to say we've taken some lovely trips that we've booked ourselves and just haven't encountered problems that we couldn't recolve on the spot. There were a couple of occassions that took the intervention of our credit card company when we returned from the trip to resolve things.

Thanks to all who have replied. We did a trip to Cancun the past year, a Club Med stay, which turned out badly. We suspect that had we set it up through a travel agent the agent, if worth their salt, would have secured a better outcome. Meanwhile, good friends who have used a particular travel agent several times with great benefits recommended that agent to us. We called and were very encouraged by her replies (including that her fee was low enough to start with and then, if we actually do the trip through her, her policy is to return 2/3rds of the fee...which could make one nervous, except that our friends vouchsafe that it's no scam; that she's the real deal, genuine).

Neither of us enjoys the planning nor has the skills or experience leading to the skills. Today we met with friends whom we plan to meet there in Lisbon and after hearing us who decided to join in, letting the travel agent work out something for both them and us. Now it's just a matter of deciding more details about what we actually want to experience while there, so also for continuing to read through this forum. All is good.