Worth spending extra time seeing Arcos, Ronda, Nerja?

I am probably prejudiced cuz I love Paris but Arcos & Ronda while lovely are good for a day each. Nerja in October may or may not have beach weather - its a hit & miss. IMHO there is not much Spain left in the Costa del Sol. I would fly in to Barcelona, spend 2 weeks in Spain then train to Paris for last week and fly home from there. It;s actually pretty easy ti chill in Paris - pick a cafe and people watch over a glass of wine. Enjoy your trip!

We spent 2.5 weeks in Spain in a chilly spring and the two night in Ronda were among the highlights. I wouldn't head for the beach but including a town like Ronda in an otherwise big city trip adds nice variety. You can see our snapshots at: http://janettravels.wordpress.com/2013/09/15/ronda-the-most-romantic-town-in-spain/
I love Paris but unless you have a week to give it, I would stick with Spain on this trip. Less is more.

One of the best things about Arcos is staying in the hotel that Rick suggests: El Convento. The view from the patio out back is breathtaking. The town is worth a day of walking around.

Arrive Barcelona and spend four nights, train to madrid for three nights, train to seville for three nights, bus/train to granada for three nights (bus transport is convenient and comfortable; do not even try and compare USA bus service to Spain). Then fly to Paris. Yes, Ronda and other small towns are great. However having five nights in Paris is a great opportunity to explore another nation/culture which provides a great perspective/balance to both Spain and Paris. Paris is uber expensive. Stay outside and use train/metro to dive in and out of Paris. Big money saver, especially when you can eat meals outside of the tourist zones.
Btw: you could fly into granada, then reverse the itinerary (seville, madrid, barcelona) and then have the option of flying to Paris from Barc or taking the new high speed train from barc to paris. Check out website The man in seat 61 for better understanding of this opportunity.

Once you've turned your thoughts toward Paris, hardly anything else compares. I would check flights now at www.skyscanner.com. You can fly from Granada to Paris for as low as $120 per person, but higher on weekends.

Most train tickets cost more than that (minimum €60 from Barcelona to Paris if booked now for a late afternoon departure in October, seats limited at that price), e.g. through Voyages-SNCF (with Verified by Visa or MasterCard SecureCode) or at www.capitainetrain.com.

Recession or not, Spain is a very rich destination. You don't describe your ages or travel experience, but I would repeat my favorite Rick Steve's aphorism, "Assume you'll return". If that means Spain, it means you can see Ronda another time. If that means "Europe", it means why spend the time and money to fly to Paris when you could fly into and out of Spain. (We just combined London and Sorrento on a trip, so who am I to preach - but this was our 25th trip to Europe.)

We loved our three days in Ronda, but that included plenty of day-tripping. If you can barely afford this trip and don't know when you might travel again, you can still argue both ways in my first paragraph: You MUST see Paris, but you also should get a taste of provincial Spain that you won't see in the four cities. If you decide to skip Arcos/Ronda/Nerja, consider visiting Carmona (and Italica) from Seville.

Why not fly from Barcelona to Madrid? Flights are almost as cheap as a train and a whole lot faster!

I just spent two months in Spain and absolutely loved it! I went to Ronda for the day and really liked Ronda and was glad I went. I do feel that 1 day was enough. I did my trip the reverse of you. I flew from PHX to Madrid, train to Toledo (overnight there - LOVED Toledo!), train to Cordoba, LOVED Cordoba! (3 nights), Train to Seville (4 or 5 nights - too long) Bus to Torremolinos (Costa Del Sol, south of Malaga) spent a month in Torremolinos. Did an overnight trip to Granada. (rented a car and drove) Enjoyed the Alhambra, wasn't crazy about the city. Flew to Barcelona from Malaga. 2 nights in Barcelona.

It rained when I was in Sevilla (Easter) and it was rainy in Barcelona. While I liked Seville and saw a lot, I think 3 days is enough. I liked Madrid best. Everyone raves about Barcelona. I spent a day on the hop on/hop off bus and saw the highlights. Many of the talked about destinations were covered up because they were being renovated so that was disappointing. This was in May 2014, but these renovations will last a while so will probably still be covered up come this October. I think 3 days in Granada may be too long there. I would highly recommend Toledo and Cordoba if you spend 3 weeks in Spain.

You can either really enjoy Spain and see a lot of it, or only spend 2 weeks there and go on to Paris. Up to you, either way it will be a great trip!