There's definitely no right answer here, although like AAupgrade I reckon half a US Cent per point is pretty poor value.

I tend to redeem at between 1 UScent to 1 UKpenny, with a general rule that I'll not redeem below 1 UScent in most cases, and always redeem at 1UKpenny. Between the 2 lies the question of earn rates, origin of points, number sat in my account and opportunities to redeem in the future.

For instance as a UK resident I'm planning a big Canada/USA Roadtrip with the teens this summer, spending 27 nights there (some with relatives) and booking a total of 52 hotel room nights, using a mixture of 300k IHG points and 600k Marriott. It'll clean me out on both schemes.

I value IHG at lower than Marriott and some nights I'm redeeming at only 0.5UScent per IHG point, other nights are closer to 1.5UScents per IHG point. I take the view these points were really free of charge, all were obtained whilst staying for work, so for my work stays at IHG I'm getting $2,500 of free nights for 300,000 completely free IHG points.

My position with Marriott is different, some points arise from work stays, others from leisure, and others still from Credit card and megabonus. Since when considering my leisure spend I do take into account the points as a 20% rebate comparing Marriott to other possibilities, I need to ensure I get that back from that tranche of points. As I actually receive 25 points/£ (after taking into account tax, credit card, arrival bonus and Plat bonus) I need to redeem at least some of this at 1UScent per point. During this Roadtrip I am redeeming Marriott points at between 0.8UScent per point (a rate I have never before entertained) and 1.8UScents per point, spending 600,000 points exactly redeeming $9,000 of room nights.

To make this decision I have taken into account the entire redemption value, the fact that many of the points were genuinely free from work stays, megabonuses, and Credit Card spend. And the fact that if I don't redeem this stack now, all it will do is sit in my account busily depreciating since I have no other family trip planned this year, or early next.

Your Barcelona redemption is half a cent per point and there has to be better value out there, though as CJKatl has pointed out, it depends on your circumstances, if all your points are from work stays and you have a huge pile, I'd redeem and save the cash. If this is the only vacation you're likely to take for a couple of years or so I'd again redeem, nobody really knows how many Muckle $$$ a pile of Marriott Mickle points is going to be worth in mid 2017!