Only in the sense that everything we "know" about the world is speculation, inferred from our fallible senses by way of our fallible reason. The world may not actually exist, after all, being pure illusion. A common Vedanta belief is that the whole world is just a dream Brahman is having which will vanish when he wakes up. Even if the world exists, you might be dreaming right now, and I might not have actually replied to your comment. Perhaps you have been in a coma for years, your loved ones desperately hoping you'll wake up, while you dream about posting poorly-thought-out comments on a web site.

But actually there are rather solid reasons for believing that the alterations in the Rig Veda over the last 3000 years have been minimal, going far beyond what is commonly described as "pure speculation". Some of them have been described already in this thread, but there is an extensive academic literature on the topic, much of it linked from the Wikipedia article you started reading.