I’ve been listening to the audio recordings on wheelockslatin.com. They speak in a monotonous moan, especially when long vowels are involved. I feel like the ancient Romans, sitting around the forum, gambling and fondling women, would not speak in this migraine-inducing drone. I always imagine it pronounced more like modern Italian (which is vulgar Latin). Although personally, I prefer the anglicized pronunciation that you see in political science and the like.
Check out some Czech or Hungarian speech on You Tube. These languages have phonemic vowel quantity distinction, but the difference between long and short vowels is almost imperceptible to those who aren’t trained in those languages. On the other hand, native speakers presumably have no trouble distinguishing vowel quantity. I would imagine that in everyday speech, Latin and Greek would be similar.
However, on the stage or the rostrum I imagine that actors and politicians might exaggerate vowel quantity, as well as other features of the spoken language.
However, we don’t have recordings of ancient Romans speaking Latin.
I, too, tend to start with Italian, but changes have evidently been vast and have to be heeded carefully. Of course Italian is “Vulgar” Latin, but so is French, Galego and Logudorese, which makes the term terribly cumbersome to apply for modern languages.
I must add here my mother tongue, Finnish (and note that Hungarian a and á, e and é also have difference in quality, other vowels being differentiated by quantity alone). This does indeed make it easy to pronounce e.g. pōpulus and populus, uēnit and uenit differently. We may in our turn have problems elsewhere: apparently Latin ĕ was pronounced [ε], a phoneme we don’t have.
And all pronunciation features are tough to catch for foreigners in random speech on television. In that sort of random speech it can often be tough to catch what words are being said, much less vowel length. Instead, try listening to someone speaking to children. For example, you should be able to hear many of the vowel length contrasts in this Czech version of Der Salzprinz:
I imagine that like adults of all regions and languages throughout history, Roman adults spoke more slowly and with more precision towards children. And towards non-native speakers.
If you want to learn a language feature, listen to someone speaking slowly and precisely. If you want to hear Czech vowel length, find a Czech doing the same. It’s not surprising if a language feature is imperceptible in random speech with no study. Nearly all language features fall into that category. In Czech, vowel length is actually somewhat prominent in slow precise speech.
Baby talk is another phenomenon entirely – and not present in the video that I linked – baby talk is probably also related to language acquisition since it is nearly universal among mothers, indicting some biological urge.