The publication of special issues constitute an important yet underinvestigated phenomenon of scholarly communication. In an attempt to draw attention to the proliferation of special issues, Priem (2006) suggested that their commissioning has an underestimated opportunity cost, given the relative scarcity of publication space: by distorting the “marketplace for ideas” through the commanding of pre-selected topical distributions, special issues undermines the total research output by “squeezing out” high-quality but topically-unrelated articles. The present paper attempts to test this hypothesis by providing a topicality and research impact analysis of conference-based, monographic, and regular issues published between 2010 and 2015 inclusively and indexed in Clarivate Analytics Web of Science. Results show that titles and abstracts ofarticles co-published are topically closer to each other than those co-published in regular issues, which suggests that their relative importance might influence the total topical distribution. However, disciplinary and overall comparison of relative citations for both special and regular issues shows that intra-issue averages and variances in the former case are respectively higher and lower than in regular issue context, which undermines not only the above-mentioned hypothesis, but also the belief that editors often “fill up” special issues by accepting substandard papers.