Yes, they need to be pronounced clearly. ed is for past tense, so if you do not say it clearly, people will think you are talking about "the now" for instance, if i were to say "i want that shirt" people will know i want it now. if i said "i wanted that shirt" people will think i dont want it now, but i did want it. get it? im not sure where "-st" is used, but it should probably be pronounced clearly too. if you give me an example of a word, i will tell you how important it is to be clear.

HI! I´m studing phonology and i must say that yes, those sounds must be pronounced clearly because they affect the meaning of the word you want to say, for example verb tenses; it´s not the same saying "i love you" than "i loved you", don´t you think?