to plan to do sth. vs. to plan on doing sth.

[Jens]

Is there any difference:

/1/ "We're planning to spend the summer in Spain."
/2/ "We're planning on spending the summer in Spain."

What about:

/3/ "We plan {to spend, on spending} the summer in Spain."

I suppose the present continuous (/1/, /2/) is preferred in this context, but would /3/ still be natural? What's the difference?

 

[Mister Micawber]

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They are all natural, and essentially synonymous, Jens. The present continuous reflects the speaker's greater interest and feeling of immediacy about his/her statement. 'Plan to' (to me) suggests a more solid plan than 'plan on doing', but the difference is minor if real.

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