My honest opinion is that if you can be understood and you aren't trying for a career in espionage, then don't worry about your accent too much. I, personally, enjoy listening to people with accents even if I have to work a little harder to understand everything being said. Anyone who wants to understand will put in the effort to listen and process almost no matter how thick your accent is. Working on pronunciation is always a good idea but being understood is really what your ultimate goal should be. Again, my opinion. :-)

Hardly! I love all foreign accents and the Spanish accent is doubtless one of the more pleasant accents. I especially like how guys really emphasise the letter 'R' and roll it on the tongue like 'rrrr' aha. It is an ineffable pleasure to hear. And no, the accent is quite intelligible; no difficulty in understanding at all.

I agree with the other members. As long as your first-language habits don't make your English speech difficult to understand (ie. you are not mispronouncing English words), then there's nothing wrong with sounding Colombian when you speak English. The accent is quite pleasant, and hopefully that doesn't distract the listener from paying attention to your message. ;) Yes, with some work you can reduce your Colombian accent in English, but that's entirely up to you. If you're still doubtful, would you consider recording about 30-60 seconds of audio, eg. on vocaroo.com, and posting it on italki? Members here are happy to give constructive feedback.

I'm with Seth, unless people find it hard to understand you don't bother.

Many of my friends and customers are European, and I appreciate their languages and accents. We enunciate our speech, and everyone has an easy time communicating. Don't sweat it.