Caps definition on rtpspeexpay element is not following
gst-plugins-good/gst/rtp/README where it says that clock-rate should be defined
as a int value (not a range). Another issue is the payload type value that
should be set to "payload = (int) [ 96, 255 ], " (or 96 to 127 - see
http://bugzilla.gnome.org/show_bug.cgi?id=324011) as speex has a dynamic payload
type.
The clock-rate should be set to 8000 as it seems gstrtpspeexpay.c only encodes
rtp packets with this clock rate. This is necessary in order to build a valid
SDP using the speex payloader caps.

static void
gst_rtp_speex_pay_init (GstRtpSPEEXPay * rtpspeexpay,
    GstRtpSPEEXPayClass * klass)
{
  GST_BASE_RTP_PAYLOAD (rtpspeexpay)->clock_rate = 8000;
  ...
}

static gboolean
gst_rtp_speex_pay_setcaps (GstBaseRTPPayload * payload, GstCaps * caps)
{
  gst_basertppayload_set_options (payload, "audio", FALSE, "speex", 8000);
  ...
}