It depends what you mean by 'Downs test'.
Here the default offer is the two non-invasive tests (NT scan and triple blood test). You can opt out if you want. You can also ask for either of the two invasive tests (chorionic villus sampling <14w, amniocentesis >14w).
Since the NT scan is much more accurate when taken in conjunction with the blood test, and since there is no risk at all to the baby, we will have both of those. We'd be unlikely to take the testing further. We would rather prepare ourselves if possible - if it turns out our baby has a chromosomal disorder incompatible with life, and is unlikely to make it to term or more than a couple of days after birth (
this doesn't happen...) we would rather know that than allow ourselves to get too excited. If the baby is high-risk for DS, then we'll just accept that risk and take whatever we're given. It's not just DS that the hospital tests for, however, but other (fatal) chromosomal disorders, and knowing people who had a baby with a serious chromosomal disorder, who died just 3 days after birth, we're both aware we'd much rather be prepared for that. Our friends had to go back home to a freshly decorated and kitted out nursery, welcome home banners, and no baby.
I guess some people like to be prepared and others would rather not think about it in advance; it also depends on your interpretation of 'high risk'. Personally, I wouldn't be too bothered by a 1 in 200 risk, but if it was a 1 in 2 risk, I'd much rather know.
I might well feel differently if the only test on offer was the NT scan by itself; and if my hospital didn't offer the NT scan or blood tests, just CVS or amnio, I'd definitely say no.